The prettiest would probably be Infinity Blade 3 but I refuse to spend 6$ on a tap and swipe game no matter how pretty it is.
If you like racing games, Asphalt 8 is a pretty good looking game and free.
I've become hopelessly addicted to Clash of Clans. May not push the graphical limits of the iPad Air, but it runs great and is pretty fun.
I will have to check that one out then!