When I was there three years ago, we stayed the Allegro. But I understand that it is no longer open.
We dived with Dive Provo which I liked a lot, though I was a relatively new diver then, so wasn't a good judge of how good a dive operator was. Dives didn't seem cut short, but my air consumption was lousy. I do remember that they handled your gear for the week, rinsing it each day and putting it on the boat for you.
The best dive sites were at the Northwest Point (almost an hour's ride from Grace Bay) and West Caicos (an hour and a half away). I don't know if there are hotels on that side of the island, but if you're trying to make a non-diver happy on this trip, you should probably stay in Grace Bay. One option may be to drive across the island and board a boat closer to the dive sites.
-Mark