Sid Meier's Alpha Centauri/Factions

All factions have distinct advantages and disadvantages. They have different society traits, start with different technologies, and sometimes even have oddities such as smaller maximum base sizes. This means that every faction has a different overall playstyle, although some factions are more suited to some playstyles than others. For instance, the Hive is more likely to ICS than the Peacekeepers, because Yang gets free Perimeter Defenses but little energy income, while Lal can get more population per base and may want to take advantage of it.

The game settings can enhance or reduce the advantages and disadvantages of each faction. For instance, disabling Blind Research weakens the aliens of Alien Crossfire because they never have Blind Research, so they lose one of their inherent advantages (Or rather, non-alien players gain the same advantage the aliens already have). Likewise, Svensgaard would prefer a world with massive oceans (essentially more territory for him) and arid terrain (which hurts land factions much more than the sea-based Pirates), while all other factions would probably prefer the opposite.

The factions
A table comparing all the factions follows. Note that a faction's "preference" is preferred by the AI but a human player can (and, under some circumstances, may want to) use something else. However, the faction's aversion, if any, is always enforced: a player may never choose a faction's aversion. It simply will not show up in the Social Engineering table.

The expansion pack, Sid Meier's Alien Crossfire brings seven new factions, which are covered here.