any boat trip to the Palencaar Reef is worth it. I would think that a catamaran trip would be fun, we went on a regular power boat. The reef is totally amazing and so each to swim and snorkel.
suggest you contact eduardo at www.cozumelsports.com, we were there in feb., had 4 of us, small boat with eduardo and our own captain, $35 per person, 9-12:30/1pm -- a real blast going to 3 reefs without a thousand people on our boat...