Dog is a definite number one. Always. For a tech character- Jayna is almost irreplaceable, with her knowlege of Therapeutics. Magnus comes second, as he gives you eye gear and feather weight axes. And, of course, Sebastian, who can make and even throw grenades. For a mage- Dante, the best melee fighter among the mages, and princess Raven- give her Ellumun's bow, and she becomes more deadly than a half ogre with a big sword. Waromon the lizard is also an awesome archer. Half ogres are good for any party, tech, melee or neutral, but I usually prefer Sogg over Chukka.
It relly depends on your character. You really don't want evil characters in a good party, I believe most won't join you anyway. Right now I'm playing good characters and keeping the alignment at 100. I save some plus alignment quests just incase it falls below 100 I can do the quest and get it back to 100, but thats just me. As far as followers go I get my charisma to 20 early and expert persuation (to get an extra follower), Then I get 10 followers. The 6 + the free four. I also try to get the followers at one level lower than them except dog (in ashbury) which I get after virgil, sogg and jayna. Just take train from blackroot to ashbury. Then I get magnus, gar, dante, chukka, thorvald, Then jormand. This is as far as I have gone but everyone has helped out especially chukka who get to str 26 or better. I don't really do any fighting, I let the party do it because the exp level doesn't go up as fast. So the best thing is just play around with the followers and see if they help you out. It can be a long game (if you want it) so enjoy adventuring and I hope you find lots of goodies. Parmanian said that PS.....Buy the way if you have a slow processor, or video card, performance will really slow down with the more followers you have. My 3 gig machine doesn't have a problem........yet