I'm quite fond of Emolga, Marill's line, and Pachi. The latter saved my butt in Reborn so many times, I've grown to appreciate its ability to troll in the right circumstances. Plus, I like squirrels cx
Plusle and Minun were favourites of mine in the early days of R/S, and although I'm not really a fan of theirs anymore, I can't outright dislike them either.
That leaves Togedemaru and Dedenne, though I have nothing against the steel-electric ball thingy. On the other hand, Dedenne looks way too much like a mini-Raichu and isn't as effective as it should be considering the typing.
I don't count Pichu, as it is a member of the Pika family. However, if I had classed it here, it would be high up on my favs list.