Having done both, you see far more, and more variety of, wildlife while scuba diving. The SNUBA or extreme snorkeling options from DePalm and Red Sail may be an option as well. As for preferring the wildlife to the wrecks, you will find that the wildlife often congregates at the wrecks. Getting your dive certification before going isn't necessary but it would give you more options, once you get there. The best coral formations are at a depth where storms haven't damaged them and it can be difficult to free dive (snorkel) to see them.