Gamefreak will troll and make the final stage for Chespin and Froakie Grass/Fighting and Water/Fighting, respectively. Whereas Fennekin will be Fire/Dark.
Now, with every new game I tend to pick the fire starter as fire types tend to be rare during the game. However, I break from this if on of the others is exceptionally awesome looking, like Turtwig in gen 4. Indeed, this time there is one that I really like - Chespin! It looks like it has a lot of character.
As for the others, Fennekin just seems too bland and boring, while Froakie just looks a mess.
Think I'll be going with Chespin, although Froakie is growing on me and I've always hoped for a frog starter. I have ten months to decide. Fennekin looks nice enough but doesn't really appeal to me or excite me in any way.
I am going to avoid the evolution lines because it's much more fun playing through the game with the element of surprise. Here's hoping Chespin evolves into a badass!
I adore Fennekin. I know I'm going to name him or her FireFox when I get X and love it to death. If Fennekin however get's horrible final forms for some reason I'd probably then go with Froakie (unless they reveal an even better water type then I'll pick Chespin). I like them all, but Fennekin is the one I love more than anything.