Well, I think that cements the Water-Rogue, Grass-Warrior, Fire-Mage debate.
Chesnaught is Grass-Fighting, so Breloom and Virizion have some competition. He's also likely to be pretty bulky with all that armor. Also, is that a Protect + Damage Reflection move he's got?
Delphox joins Victini and Zen Mode Darmanitan as Fire-Psychic.
Greninja is apparently going to be Water-Dark, though no picture of that.
Chesnaught = 6 Resistances, 6 Weaknesses (x4 from Flying Moves)
Delphox = 7 Resistances, 5 Weaknesses
Greninja = 6 Resistances, 5 Weaknesses, 1 Immunity.
It looks like Chesnaught is going to need that bulk, being the only one of the three with a x4 weakness, an extra weakness, and fewer resistances (once you factor in the immunity that Greninja has). While it does get some good resistances (Water, Electric, and Grass), it also picks up some quite common weaknesses, especially if Fairy is common or Poison actually does become more heavily used.
Delphox looks to be the only one not weak to the new Fairy type (in fact, it resists it), and depending on how overboard they go with their shiny new addition, that could easily be an advantage.
Greninja seems to be about average, resistance wise. Nothing great, and nothing really too devastating. It's weak to Fighting and Fairy, which could hurt it late game or competitively, but for most standard play, it looks like the weaknesses and resistances cancel each other out.
I think I'll be among those choosing Froakie (and trading myself the others from my second game).