I guess I'll go with the flow and go ahead and put a list out... I don't have much knowledge with the EU, so be merciful
Ok, Sith: Darth Plageuis seems like a nice idea, or Darth Revan (I know nothing about his source material, but he seems HUGELY popular, especially in this game, though his original piece is near-useless)
Old Republic: Maybe the Grand Master (Vandar, is it?)? One I don't know much about...
Seps: My favorite faction... They seem to have been milked out of most decent epic options... I'm wary to suggest an EPIC Grievous (it would be so different probably, how much can you juice a guy like that and make it work, and compete with these other epice? Hmm...), though he is my favorite character, and PROBABLY their best option atm (or maybe some mega-powerful battle droid or some kind lol). I know better by the feedback I've gotten on this MISTAKE before than to suggest a Seps Anakin
.
Republic: Not Kit Fisto, Master Tiin or that other guy who got slain by Palps within seconds with a FOUR TO ONE advantage. Anakin Skywalker WAS the Chosen One... Maybe an EPIC for him is in order?
Imperial: I don't know much about the EU after episode 6, so I don't know what one would do with this spot... Maybe this Inquisitor dude from the new TV show will be good enough for consideration?
Rebel: Han Solo definitely would be a nice choice, can't think of anything atm that would be more fitting (but there aren't many non-melee EPICS at this time)
NR: Not sure about this one either, but I'm going to guess that 'Luke Skywalker again!' is NOT the correct answer.
Mandos: I've always been intrigued by Canderous Ordo, not sure if there are better choices though.
Vong: Shimrra. From what I know, he's the guy.
Fringe: GRIEVOUS
. I mean, he was ONLY an incredibly renowned warlord who single-handedly turned the tide of a war. As far as other possibilities, in Fringe there are soo many I can't think of any good ones atm. We already have Boba in the Mandos, so that wouldn't work.