fishi gave good information. The problem with asking for "any advice" is that you'll get hordes of people all advising their favorites and you'll still be left with 20-30 dive ops to choose from.
Personally, I like the "boutique" dive ops that provide more service and smaller boats. Many will retain all your dive gear between dives so you don't have to drag it back and forth, offer larger tanks so you can easily get 70-90 minute dives, and hopefully attract a more experienced clientele so you're not limited on the dive sites. They cost more, but you get more bottom time so your cost per dive hour is about the same or actually less even with the additional services provided.
Aldora is the most popular of these types of dive ops. Being one who goes against the crowd, however, I prefer a smaller op called Living Underwater where you usually get to dive with the owner himself, the best guide I've ever had the pleasure to follow underwater. So, counting Allison, that makes 3 so far. I'm sure others will chime in with their favorites.
I'm staying at Secrets June 14-18, then relocating to the Cozumel Palace. If our dates overlap, I hope to see you there. There's a June "roll call" thread (Back to the Summer) with a developing list of divers on island that month. Feel free to add your info their once you figure out who you're diving with. It's often a good way to meet a friendly face.
