Megazard Y like said, can come right out of the gate and hit VERY hard as a special attacker.
Flamethrower, fire blast, heat wave, solar beam. All special and all can hit pretty dang hard.He works perfect as a sun setter and sweeper.
Megazard X's tough claws screams physical sweeper, and the way to get those is through egg moves and more work.
While Megazard Y is my favorite of the two, I kinda like Megazard X. It's what the fans have been asking for for years. Personally, I just wish they didn't change up his colorscheme so much. Or at the very least, making Shiny Megazard X look like normal charizard.
At least Shiny Charizard looks fitting turning into Megazard X.