Border Tactics
Assault
The best bet for assault it so run the North path into the city (or over the hills to the North of the Town Hall). It's the hardest for Defense to defend against. Remember, this is a sniper's dream map, so stay moving in random directions, and try to stay under cover. If you choose to go South of the Town Hall, take it slow and easy, and scan constantly.
Defense
The best place to cover the Southern passes is to enter the building with the two windows and crouch. If you stay stationary in the crouched position, especially on the right side, your head is almost invisible to their rushers. Scan the hills and the South pass and take out any assaulters, and watch out for a flank later in the round.
The next best place is the balcony to the left. Not as much cover as the first position, but definately worth sending an extra man.
Covering the North you have many options, but all get you picked off rather quickly. There are the walls/destroyed buildings to provide cover. Keep an eye on the hills, the Town Hall, and the destroyed building.