A bunch, but mainly...
Trubbish! *_* Look at it! It's SO CUTE, and somehow being an animate bag of garbage just makes it cuter!! I'm a bit more lukewarm on Garbodor, but I still like it!
Jynx! Sure, it's design is vaguely creepy, and it's weird to think of using a Pokemon that's
so human-like - but, in my opinion, that's the point. It's a Pokemon based on
the uncanny valley! I love that!
Carbink! I like its design, and how it basically serves as a royal guard for Diancie - but what really made me love it was its Y Pokedex entry:
It has slept underground for hundreds of millions of years since its birth. It's occasionally found during the excavation of caves.
...I
love incredibly old beings like that! Especially when they're cute and unassuming! Haha. Also, contrary to what people say, it's been so good whenever I've used it in a playthrough - an absolute wall.
Ice types in general are less loved than the other types and I think Glaceon is overshadowed by its eeveelution siblings.
...Huh, Glaceon is also my favorite, and I always thought it was one of the more popular ones.

Maybe I'm just out of touch.
On the same note, Flareon is pretty high on my list of favorite Eeveelutions.