Depending on how much you want to spend, what you like to do when not diving, how much diving you want to do, you have any number of choices in GC.
We are big fans of Cobalt Coast, which is towards the north (not terribly far from Spanish Bay resort). If you like the "big resort" feel, it might not be for you. It is a small, excellently run hotel -- we liken it to a land based live aboard. No beach, but a great pool for relaxing in after diving. CC offers a couple of meal plans (the food is quite good) or if you have a car its not that far to drive back down to seven mile beach. The rooms are roomy and typically feature a refrigerator, so you can keep beverages and snacks on hand.
The dive op connected with CC is Divetech and we love them too! In addition to the boat dives, which typically do the north wall if conditions permit, you have a great shore dive right off the dock at CC and at Divetech's other location, Turtle Reef -- and you can generally find someone at Divetech to give you a lift over to Turtle Reef for your afternoon dive.
If you prefer being in the middle of things, I've heard good reports about the Westin. If you do a search, you can probably find a lot of additional recommendations for other GC accomodations and dive ops.
sdwho