>>19143180Both are equally good, actually. Just on different levels
X has unresisted, Tough Claws boosted STAB bar Heatran and Carbink (which can easily be countered with Earthquake) across the board, and once it gets a Dragon Dance in it's nearly unstoppable
Y requires no set up and has STAB Drought-boosted Fire Blast and Solar Beam to nuke almost everything in sight. Not even the bulkiest Rock-Types can take it down without trouble
tl;dr both Charizards are good and that makes it even more lethal