There's only realy two choices of mainstream dive ops out here Bahama divers and Stuart Coves. BD is a bit more relaxed and quieter. SC's is very busy since they run snorkel, sub experience, resort dives and at least two scuba boats every day.
Best advice? Try both. BD's has alot of shallower reefs and the lost Blue Hole (extra $20) SC's has the Wall, Shark dive and a plethora of wrecks.
If you can stand the pace of coves, (it does get busy) that's where you'll find a vacation!
BD has the dive shop (expensive) and is closer to Paradise Island. Cable beach and it's resorts are about equidistant to both set ups.
SC's is better diving. I'll defy any one to call me on that! If you get to Ray of Hope on a calm day, get to plummet over the wall with sharks all about and still ascend to investigate the 120 foot wreck right next to Bahama Mama (another wreck) all in one hour long dive!! you cant go too far wrong!
But try both if you've the time. The bus ride to SC's is a killer.
Up side? you won't go wrong in either case.
Enjoy!