Mesmerize was just the better album if you ask me. Definitely my favorite album of theirs. They got a lot more creative than other albums and explored some musical directions I never would have expected from them. It's also one of a dozen or so albums I own that I can honestly say I love every song. Hypnotize was great as well though. Some of it's songs really stand out, but overall I'd put it just behind Toxicity for a solid third place in my ranking of SOAD albums.