Our first dive trip, a month after certifying in a hot spring in the middle of nowhere, USA, was to Cozumel. The diving was not overwhelming or overly challenging in its difficulty, and the life and topography below was stunning. We figured out drift diving by the second tank. We did swim-throughs at 80-some feet. If you're comfortable with your skills and can follow a divemaster's directions, I say go for Cozumel (which I personally would rate way above Belize, unless you do some pricey atoll dives like Turneffe, Glover's, Lighthouse, etc.). Why wait?