I honestly have no idea. It's a bit early for me to decide - it's something I'll probably plan out closer to the English release date. Though I have decided that, if I don't do a challenge for my first playthrough, I'll stick to trying to use Pokemon I've never used before, since there's still a lot I've wanted to try in Unova. I've also decided to limit my use of pre-Gen V Pokemon down to 2 at most.
Some Pokemon in particular that I want to try are Durant and Hydreigon, and an Eevee evolution that I've yet to use (I'm leaning towards Jolteon at the moment), but I just don't know at this point.