Now that we know all the starters, here are my collective thoughts:
Delphox has the best typing, but the worst design.
Jagernut has the worst typing, but the best design.
Greninja has solid typing and solid design.
Only things left to see are the stats and movepool, which Greninja is on top of as far as we know. We'll see what more information we get. Hoping Jagernut is extremely defensive.
EDIT: Apparently the name is confirmed to be "Chesnaught."