Drifblim, definitely. It's really hard to choose, though, since I love Mismagius, Rotom, and Dusknoir too... [Can you tell what my favorite type is?]
I loved the idea of a cute Ghost-type at first, and then I raised one and found out that it was awesome in battle. :D At the very least, in my opinion. It's funny, though. Dusknoir is the evolution of one of my favorite Pokemon ever, but I can only admire it from afar since I've never really gotten to know it. :[ One day, though, I'll finally get Wi-Fi and trade one of those suckers over~