Just about all the dive shops on the island are the same. Every one of them offer Open Water, Advanced, Rescue; each for around $160. (10 fun dives for around $125). (Divemaster $500). The only difference is the little perks you get. Utila Diving School and Gunter's both include 2 free fun dives. Bay Islands College of Diving has really nice boats with bathrooms and pastry buffets.
I heard that there are some shops that cut corners, but I didn't hear which ones. The three mentioned above are supposed to be good. I dove with Gunter's because they also had kayaks which were free to use for their students. They have a web site at www.riconet.de/ecomarine