Daaaang. I love both so much, too. D:
I love them both, and I'm a history nut, and I love that they're both involved with a big part of the history in Pokemon, but Cofagrigus looks like he used to be a king, and I have a soft spot for ancient royalty.
I'm going to have to go with...Cofagrigus. Such an awesome physical wall, amazing defense, decent Special Attack, and a pretty nifty movepool. Plus, I love that I feel like he's about to tell me "RETURN THE SLAAAB, OR SUFFER MY CUUUURSE."