I've had favorites, like Luxray, Lucario, and Umbreon to name a few, but now there's Noivern, which I think looks freakin' awesome. Found some epic fan art here: http://fc08.deviantart.net/fs71/f/2013/162/e/d/noivern__by_biancascrafty-d68mwir.png
I have lots of favorites, and I even admit I was an original Charizard fanboy, but so far my current all time favorite Pokemon are Tyranitar and Hydreigon. I fell in love with both the first moment I saw them:
Tyranitar's debut in that Celebi movie
Hydreigon when I was skimming the BW Pokedex on Serebii for the first time.
Official hot fudge sundae of the IDF Official Hydreigon of the Pokemon B/W 2 Boards.