I think the better companios you can get are:
The jedis, obviously, are very good. Bastilla was quite helpful in many situations, and i think Jolee Bindo is one of the best to have around. Aside from his always funny comments, his force powers are quite good and always have lots of powers to help me out.
Haidmaiden is also pretty helpful, especially in close combat. Kreia and his powers also help a lot. I also think Canderous is helpful, as HK-47 fully upgraded.
By the way, i think KOTORII sucks close to KOTOR. The plot is a big bullshit, there no realy worthy turning point, the end is crap, your character is just overpowered by the end of the game (i hate when characters in godly mode), etc, etc, etc.