Xerneas is so much easier to remember.
...and say.
...and spell [for me anyway].
Yveltal, I didn't know how to pronounce that at all until I saw the pronunciation on Serebii. They're just names though, and eventually we get used to them. Except in the case of Gen V, where I still don't remember half the Pokémon from that region.
These have definitely been my favorite pair of mascots for quite a long time now. Probably since Groudon, Kyogre, and Rayquaza. I'm just glad we seem to finally be moving on from the Dragon-era of Pokémon mascots. It's about time if you ask me.