Alphonse Graniel ("L'il Alphonse") is a fantastic guide on the reef. His Shark Ray Alley/HolChan Reserve is a fun 1/2 day tour. I booked through Monkey Business Travel, located at Banana Beach Resort the evening before. One day I found I had unexpected free time so booked Alphonse again (!) right before lunch for his afternoon excursion.
You have to go with Alphonse!!! He was great! My wife and I went to the Hol Chan & Shark Ray Alley with him on 11/1 and we had such an incredible experience we booked the Mexico Rocks and Tres Cocos the next Saturday with him. Both were great. You get more than you pay for. He is very enthusiastic about his job.