I really enjoy playing Peacekeepers, coz of their neat extra talents thingy.. it keeps the drones away for a while. I have also played some with the Spartans, but I think they're boring, even though I don't know why..
I've never played with anything else, but the Gaian worm thing sounds kinda cool..
One thing: all you who play University. When you play as something else, have you noticed how stupid the scientists act? They always gets their little asses beaten by the Belivers(who I hate, and always try to obliterate as soon as possible..). The Hive also picks on the too-quick-expanding University..
Another really cool thing about the Peace dudes, are that they get double votes in Planetary Governor and Supreme Leder elections. Combined with the Empath Guild and that other secrect project that doubles your votes, you are instoppable.
I have now (this is a edit) payed some with the Gaians, and... WOW! I don't think I'll ever play anything else (exept for the Peacekeepers.