Hitman: Blood Money/Weapons

Silverballer
The one must have piece of equipment. While the other weapons in 47's arsenal do have their uses, few are as precise and deadly as the Silverballer, especially considering that most of your kills will happen at close range. Most of your emphasis should be on silence and accuracy, so acquire silencers and aim stabilizers as soon as the upgrades become available.

Upgrades

 * Low Velocity Ammo: Essential. More silence and less recoil - both advantages.  You'll probably have this upgrade through most of the game, if you want to be as silent as possible, so make sure to get it early on.
 * Silencer Type 1: A good early silencer for your weapon. Excludes Silencer Type 2 and Long Slide, but you don't need to worry about those for a while.
 * Extra Ammo: You usually won't need to fire more than 2-3 bullets per mission if you play strategically, but extra ammo is always handy just in case.
 * Laser Sight: No reason not to get this...the little targeting dot on the back of your enemy's head is useful when firing from medium range.
 * Rail Mount: Does nothing on its own, but the mount is required for scopes or red dot sights. Not worth buying early now on until you actually unlock a Silverballer scope or red dot sight for purchase.
 * Magnum Ammo: Noisier and has more recoil than low velocity ammo, but it can penetrate doors. However, if you need to fire through doors, than you should probably be using a weapon more powerful than the Silverballer.  Still, it can come in handy when you're attempting to shoot enemies that are pursuing you when you can effectively use a door as a barrier.  In any other situation, you're unlikely to know that someone is even on the other side of the door.
 * Dual Action: The ever popular dual-wielded pistols. Unfortunately, these two guns fire simultaneously when you pull the trigger. That's great if you need to drop someone who's aware of your presence, but if you're aiming for a stealthy headshot, that's one bullet which misses, and the resulting noise may very well alert other enemies of your position.  If that's what you're attempting, you're much better off simply using a silenced .45 pistol.  Another con of this upgrade is that it effectively doubles your gun reload time.
 * Long Slide: Gives better precision and less recoil....but it can't be equipped at the same time as a silencer, making it a somewhat pointless upgrade.
 * Red Dot Sight: Provides a small amount of zoom and better precision, but it unfortunately can't be used with a scope. Still, it is a good idea to equip this until you unlock the scope with the last set of upgrades and use it until then, since there is no better solution available.
 * Large Clip: Very useful, doubling the capacity of your clips, although not a good upgrade if you want to play strategically with only 2-3 bullets to fire each mission.
 * Silencer Type 2: Maximum silenced. Essential for a stealthy approach involving Silverballer(s).
 * Full Auto Fire : This upgrade adds recoil and lets you choose to fire automatically, shooting 3 (6) bullets when you pull the trigger. If you're using the Silverballer with extreme care and precision, opting for headshots, then this is going to be overkill, plus using it incorrectly will empty your clips very VERY fast.  If you intend to upgrade it to the point where it becomes SMG-like...why not just use it as an SMG? Probably one of the worst upgrades.
 * Scope Type 1 : Oddly named, as it is the only actual Silverballer scope you can buy. It gives a bit more zoom than the Red Dot Sight and better aiming precision.  It's not exactly going to turn your Silverballer into a sniper rifle, but it'll allow for headshots from a rather long distance, when required.

SP 12 Shotgun
Ah yes, the ol' boomstick. Extremely powerful weapon, capable of blasting people off their feet....it has two rather big disadvantages, though.

Firstly, it cannot be concealed in your clothing, which means you'll have to pick it up from the ICA crate placed in the level after you arrive. Generally these crates are somewhere near your starting location, but as soon as you pick it up, you'll be fired upon by any guard that sees you running around...

Secondly, the M4 is a much better assault weapon than the SP 12 shotty. A fully upgraded M4 is pretty much capable of killing people across the border in the next country, while the SP 12 has to be fired from practically point-blank range to hit. The M4 can also hold much more ammo (think several hundred bullets) when upgraded, making the SP 12 somewhat of a marginal weapon.

Upgrades

 * Flechette Ammo: Allows you to fire in a tighter group, for less damage. This is the way to go, however. With most of the rounds hitting in a close pattern, your target will die, "less damage" or not.  The standard ammo will render you incapable of hitting targets standing about 10 feet away from you.
 * Butt Stock: More precision, less recoil.
 * Extra Ammo: Worthwhile, obviously. Shotgun ammo can be found in some levels, but this is for the basic shotgun, not the SP 12, so make sure you stock up on ammo.
 * Reload Boost: This decreases your reload time by mounting shells into a clip. Since the initial shotgun reload times are pathetically slow, make sure to pick up this upgrade.
 * 12 Gauge Slugs: Maximum damage, but this isn't so important. This ammo is less precise than the Flechettes, meaning that you'll often need to fire twice (or more) to kill your target, meaning that you'll be taking more damage than you would using the less powerful, but still more accurate ammo.  It is overkill, since the Flechette ammo is usually enough to kill.
 * Rail Mount: Allows you to mount the Red Dot Sight later on. By itself, no use.
 * Short Barrel: Sawing off the end of your shotgun will let you do more damage, but it will make your spread worse, pretty much negating the effects of the Flechettes and buttstock.
 * Laser Sight: Generally, your shells will land all around the laser sight, but getting the upgrade couldn't hurt.
 * Magazine: Provides four extra slugs and an improved rate of fire, which is critical when using the shotgun. Reducing the amount of time between reloads guarantees you'll be able to kill more enemies and thus take less damage.
 * Red Dot Sight: Maximum precision. That's relative to the other SP 12 sights, of course, not in comparison to the red dot sights of other weapons.  Considering the nature of the shotgun, your shells will scatter all over the place regardless.
 * Silencer Type 1: Can only be equipped if you unequip the Short Barrel upgrade. It works quite well, even though it seems quite odd to equip a shotgun with a silencer.

SMG Tactical
This is a fine weapon, capable of dishing out fully-automatic fire that will drop plenty of people. The main weakness here is a low ammo capacity; even after upgrading, you'll have a hard time killing more than a few targets without needing to reload. Still, a plus here is that the SMG can be concealed in your clothes (unlike the SP 12 and M4), making it the best option for a mass murder spree, while still retaining some stealthiness, if you are inclined to do so. In a pinch, you can single-fire a round at a target or use it as either a long range Silverballer or short range sniper rifle...it's uses are quite varied.

Upgrades

 * Butt Stock: Less recoil, more precision. It's worth buying.  However, you should note that this upgrade and the 3rd one in the list are apparently the same thing, but with different graphics...choose the one you like and don't bother spending money on the other one...unless you have some cash to burn, of course. Also one of the Butt Stocks will make your SMG look identical to the MP5, so, unless you like having two of the same weapons, don't buy it.
 * Low Velocity Ammo: Can be useful, if you think subtlety is required with such a weapon. Generally though, if you're using this instead of the Silverballer, the time for stealthiness and headshots has probably passed.
 * Butt Stock: Read description of other "Butt Stock" for info.
 * Extra Ammo: Provides two extra clips and some extra ammo per clip, quite useful.
 * Rail Mount: This upgrade lets you mount a Red Dot Sight later on, as with the other weapons. Doesn't do anything on it's own, so it is not worth purchasing until later on.
 * Magnum Ammo: Penetrates doors and does more damage than regular ammo, but has more recoil. In most cases, using the SMG, you'll probably be firing at close range, so recoil isn't such an important aspect to consider. However, if you want a stealthy approach, Low Velocity Amo is better.
 * Rapid Fire: Extremely fast rate of fire. Once again, with the drawback of having more recoil.  This will let you take down targets much faster, but will absolutely chew through the ammo, taking 5 (10 with the Double Clip) bullets when pulling the trigger, and you will find yourself reloading much more often.  Not a recommended upgrade, short bursts of fire to get headshots are generally more efficient.
 * Short Barrel: More damage, but less aiming precision. Not that important if you're only using the SMG for crowd-sweepgin if you screw up and the alarms go off, but if you need to sight a target in an area where you can't bring a sniper rifle, this upgrade becomes something of a liability.
 * Silencer Type 1: Lowers shell damage, but also reduces the chance that you will be heard firing.
 * Laser Sight: Increases precision and lets you know exactly where the bullets fired will hit. Useful and can't be negated by other upgrades, so buying it is  recommended.
 * Double Clip: This is basically two clips taped together, greatly saving off your reload time. Buy it, it might save your life a few times if you're a frequent SMG user.
 * Silencer Type 2: Better than type 1, and makes the SMG quite a silenced Silverballer, good if you are shooting a low-numbered crowd of people from behind.
 * Red Dot Sight: Provides a small amount of zoom and greater precision. As previously mentioned, this upgrade requires the Rail Mount.

M4
Like the SP 12, the M4 is non-concealable, meaning that it will be placed in an ICA crate at the beginning of the level. Unlike the SP 12, the M4 is an excellent combat weapon. Huge accuracy, power, and ammo reserves...if you intend to go through Blood Money as a FPS and not a stealth game, then this is the gun for you.

Upgrades

 * R.I.S. Handguard: Does nothing on its own, but is required for some later upgrades.
 * Low Velocity Ammo: A waste. If you want quiet shots, then this is not the gun to use.
 * Butt Stock: Less recoil, more precise.
 * Extra Ammo: An extra 2 ammo clips.
 * Laser Sight: Useful when trying to score a headshot with your opening volley of fire, but if you're generally trigger-happy, mowing down legions of guards, then this might be redundant.
 * Rail Mount: As for other weapons, this is a prerequisite for scopes, doing nothing on its own.
 * Armor Piercing Ammo: Does added damage and shoots through doors.
 * Silencer Type 1: Useless, again. The M4 is not used in a stealthy approach, better off with a Silverballer.
 * Pistol Grip: With this new grip, your aim will be a bit steadier. You'll need to buy the R.I.S. handguard first, though.
 * Double Clip: Same deal as the SMG. This reduces your reload time significantly.  However, the "Drum Magazine" upgrade will render it useless, so think twice before buying.
 * Red Dot Sight: Small amount of zoom, lot more precision aiming. However, like the Double Clip, it'll be rendered obsolete by the Scope upgrade, so you might as well save your 150,000$.
 * Silencer Type 2: As mentioned before, it's a possible upgrade, but seems to defeat the purpose of the M4.
 * Drum Magazine: 100 rounds per drum will prevent you from having to reload your M4 for quite a while. Although it has more recoil than the normal magazines, by now you should have a good deal of stability thanks to the other upgrades, so this shouldn't matter all that much.
 * Scope Type 1: The scope gives plenty of precision, but it is wasted on the M4: if you're firing at a distant target, you'll likely need to zoom in to get more precision for a headshot, and holding the fire button will cause recoil. As such, your gun will jump over the targets head.  Not really recommended.

W2000 Sniper Rifle
This rifle is going to be useful for a few game missions. It'll allow you to take down a target from extremely long distance, unnoticed (if you've silenced it properly, of course). An added benefit is that it can be carried in a customized rifle case, to be assembled/disassembled for use wherever you wish. This is much more inconspicious than running around with a huge rifle in your hands. Care is needed when constructing the rifle, as being seen in this act will raise the alarm. Generally, a single shot to the body should be enough to kill most targets.

Upgrades

 * Low Velocity Ammo: Less sound/recoil. Should be the only sniper ammo you buy throughout the game.
 * Double Capacity Clip: Useful, if you're not already using bolt action. If you have to fire 2-3 times before reloading though, you've probably already messed up any chance of stealthy sniping.
 * Extra Ammo: An extra clip. As previously mentioned, not exactly critical as an efficient sniper usually won't shoot more than 2-3 rounds in a mission.
 * Scope Type 1: Critical. A sniper without a scope is just a rifle. Get it ASAP.
 * Lightweight Frame: This upgrade able to you more precision and stability when you're aiming. The only in-game description is "light-weight parts", which is pretty vague.  Still, it's a prerequisite to the Bolt Action upgrade, so go ahead and get it.
 * Silencer Type 1: Fairly important if you silence the shots from your rifle. The quieter you are, the less likely you are to gain suspicion or guard attention when firing.
 * Armor Piercing Ammo: Allows your shots to penetrate doors, with the disadvantage of added recoil. While the recoil penalty won't be that big a deal if you're using a bolt-action rifle, there is no need to penetrate wood when firing the sniper; most snipeable targets will be standing out in the open, or at the very least, have a pane of glass separating the two of you, which can easily be shattered by normal bullets.
 * Extra Ammo: Yet another ammo upgrade. Again, you can get it if you want, but it is really not necessary as the starting ammo is more than sufficient if you snipe carefully.
 * Carbon-Fiber Barrel: Less recoil, more precision. Unfortunately, it also adds a few seconds to the rifle construction time.  If you pick assembly spots well, locations that are far away from any people with no chance of being seen, you should be OK with this.
 * Bolt Action: Gives much more precision, which is going to be important for long-range firing. You'll have to wait a few seconds between shots, though, so make sure you get it the first time!
 * Silencer Type 2: This upgrade should make your shots almost completely inaudible. "Less damage" is listed in the upgrade info, but go ahead and get it, no need to worry about this.  Even a completely un-upgraded sniper can kill any target with a single shot to the head/body.
 * Scope Type 2: "Max Zoom" is in the description. Need more incentive?