Hmmmm...nobody actually answered your question, which was basically "which two dive sites would you recommend". Assuming you're doing a single 2 tank trip, you'll have a deep dive and a shallow dive, and I would recommend trying to get to Palancar or Colombia reefs. There are several sites on Palancar, they're all great IMO, and Colombia deep followed by Colombia shallows is a classic. What the others said about the group choosing the spot is true, but you can try to contact a few dive ops in advance, tell them what you're looking for, and hope for the best.