I'll very likely have only gen VI Pokemon with me too the first times I go through the games (unless most of the good new ones turn out to be catchable much later in the game and I already get a pre gen VI one that I really like).
I'm a the Luigi master! www.freewebs.com/luigi_player/
The only ones I've confirmed to be definite for my team are from Generation VI: Chespin, Helioptile, Skrelp, and Noivern. And even then, I'm torn between Litleo and Houndour for one slot, and totally undecided on the final slot.