I went with Scuba Club, but not sure if they book divers that aren't staying there. As for dive sites, they have so many that are amazing. If you are diving for a few days, the dive master can figure out what type of places you want to go to and choose depending on difficulty level as well as water conditions during that time. My favorites though are Palancar Caves for a deeper dive with great formations and lots of life. Paradise reef is a good shallow dive and a great night dive.