I think I still like Y more. X is now vulnerable to ground attacks. Y gets a sp attack boost as well as Drought to really up the damage.
I'm preordering Y tomorrow.
Yeah but... a powerful physical dragon immune to burn. And dragon/fire coverage is incredible anyway. Only downside is he takes 50% from rocks coming in to mega evolve, but only 25% after since I believe it was confirmed mega evolutions last the rest of the battle. Maybe people will try to lead with him? Who knows.
I was getting X anyway for the fairy type legendary, and while X-zard is certainly great, it makes me worried they're going to release something even better for Y, like Sand Rush Garchomp.