Simply because ponies pokemon that evolve because of high happiness are often more powerful than those that evolve by level or stone, Imma have to go with Twilicorn.

And it has absolutely nothing to do with the fact that I *really like Twilicorn. Nope, nothing at all. I ain't lying, I swear.

I'm still hoping G6 allows an evolution for Rapidash that becomes a Winged Unicorn