Designs can suck my cock, I eventually get used to them all.
Now, which one is objectively better:
MegaZardX >>> MegaZardY
MegaMewtwoX > MegaMewtwoY
Clawitzer <<<<<< Dragalge
Sunkern > Slurpuff = Aromatisse
Xerneas >>>> Yveltal aka mr. OU candidate
CharX is fantastic, one of the best dragons available. Fire/Dragon is an amazing typing, especially this gen. CharY has its niche, but it's gonna be BL most likely(if they make tiers for megastones), sun is not that great this gen.
MewtwoX is the first fighting Uber not counting Arceus, that immediately gives it a huge niche. MewtwoY is just a slightly faster Mewtwo (and Life Orb Mewtwo hits harder)
Clawitzer is mediocre all around, Dragalge has fantastic typing and hits like a truck with adaptability
Both exclusive fairies are trash.
Xerneas is not the best uber, that for sure, but it's still great on that tier. Yveltal on the other hand is just underwhelming, people have talked about testing it in OU. I doubt it will become the next Kyurem, Oblivion wing might be a bit too much for OU to handle, but low tier Uber for sure.
