Well, for me, what usually happens is that in the first set of games for a new generation, I have only pokémon of the new generation. However, when the sequels to those games come out, I dip into other generation for my team. For example, in both my Diamond and Black games, I have strictly Generation IV and Generation V pokémon on my teams, respectively. But in my Platinum and Black 2 games, I have pokémon from other generations as well on my teams, like I have a Houndoom and Poliwrath on my Platinum team and a Claydol, Magneton, and Growlithe on my Black 2 team. I think its because, by the sequels, the shine has come off the pokémon of the new generation.
Anyway, I'll have to actually see the pokémon of the new generation before I make any decisions about it. I do have an idea of the types I want, though. I'm listing more than six because I'm assuming that I'll be having mostly double-types on my team. This is also assuming that I like Fennekin's evolutions (and that they are neither Fire/Fighting or Fire/Psychic):
-Fennekin (Fire/???)
-Grass
-Water
-Dragon
-Flying (unless I find a non-flying type that can learn Fly. Perhaps the Dragon type I plan on picking up?)
-Fighting
-Ghost
-Ice or Electric
-Dark
-Supposed new type that's being introduced this generation (just a rumor that I heard, btw)
-Maybe one the new Eeveelutions if I like them or their typing (it'd be the first time I had an Eeveelution on my team)