Probably Snow, Sahz, and Fang, as they have all come across as the most interesting characters (I'm ignoring the fact that I know the game dictates your party until almost the end). I'll probably throw Lightening in there as well.

I'm indifferent to Vanille but her fans are definetly annoying. Hope is someone who is seriously going to have to try hard to win me over cause he's just comes across super annoying in every story scene I've seen in the trailers. Not to mention his whole story in the party is a complete rip off of Ken Amada from Persona 3, its going to be very difficult watching his story unfold and not compare it to Ken (Whom I actually liked). Course I have to punch somebody cause Hope gets one of my favorite Eidolons in the series and I feel Sahz kinda got the raw deal.