I don't really have a preference for either Charizard.
I love X's design and how after about a decade and a half Charizard's dream of being a true Dragon type became real. Has a pretty sick ability too!
I don't like Y's design so much, but the massive Sp Atk he has plus Drought would make moves like Fire Blast or Solarbeam insanely overpowered.
So I can't choose one or the other, I love them both. Just putting it out there but the best Mega of all right now is Kangaskhan. Just saying! :P