From personal experience, Vector(IA) is the best imo.
Quinn(sith warr) was a close second
Aric Jorgan(trooper) is a pretty cute romance too.
Doc(jedi knight?) and Torian(BH) look pretty cute from what I've seen on youtube, haven't played their romance in game though.
I watched all of Corso's romance on youtube, and wasn't impressed. Half the time he'd start to say something good then cut himself off and say something like "I can't do it. I can't just treat you like some hutt slave dancer". Which in turn, is him calling me as bad as a hutt slave dancer since I was liking where it was going before he decided to go all noble. So now I'm dissapointed and insulted. lol