Super Mario 3D world by far.
-The difficulty curve is a bit weird, and the worlds really have not a lot of coherence. But the levels themselves are really fun, even the really easy ones.
I'd also put Rayman Legends, Wind Waker, and Pikmin 3 above it.
MK8 is very good. However there's a couple things that hurt it.
-Battle Mode sucks. (this is the biggest one). This significantly hurts the options for for fun with friends imo (which is what I mainly play this game for, racing is fun, but battle mode adds variety!).
-They went a bit overboard, I like the spinning tracks not following any dimensions with the futuristic tracks. But they went a bit overboard making too many tracks go every which way. (this is a minor complaint).
-I don't think the music is as good as SM3DW
