Y.
Reasons:
Yveltal. I like dark types. It simply looks cooler.
Y can be considered the 'red' of the 'red and blue' despite not being the lead game, as we've seen with Diamond and Pearl, it's the red game but not the lead game, but I don't care because red game for life.
Another reason would be Mewtwo is a much better Pokemon than Charizard, therefore it follows that you would want the better versionf of Mewtwo, Mewtwo Y.
Thankfully, however, my brother is getting X and we shall find a way for me to also have Charizard X, a Pokemon I favour for its dragon type.
Further justification, found after the intial decision was made, is that Skrelp and his evolution are infinite better and so are the other Y exclusives I've seen that aren't Mega Charizard Y.
Y also received some hipster cool points for inevitably selling less copies.
Row row fight the Matriarchy.
