As far as activities and amenities, it would help if you give more details what exactly those are for you.
There are only a few dedicated dive places on GC where you would be diving with their operator and be able to get on a boat or do a shore dive on site. In some cases those places are missing things you're probably looking for, like a beach. If you decide not to go for one of those then diving-wise it doesn't matter as much where you stay as long as you select the right operator who dives the better areas and will pick you up where you're staying.
As far as access to the best diving, that would be the East End or the North Wall for the most part.
On the East End there are only 3 resort options, I'd stay at the Reef and dive with Ocean Frontiers. Ocean Frontiers is located not far down the road at Compass Point condos, which are nice but not a great place for non divers. But OF will pick you up or it's a short drive. The Reef has a very nice beach and pool, pretty good snorkeling, some activity, but if your non divers want lots of activity/shopping/restaurants all the time it's a long drive. There is also Morritt's Tortuga Club next door.
In the northwest, Cobalt Coast is a very nice place to stay and the excellent on site op DiveTech dives mostly the North Wall, or the northern end of the West Wall when weather blows out the north side. It's a smaller place in a quiet area and there is not a lot to do for non divers at CC though. Nice enough pool area but no beach (rocky coral shore) and nothing much in particular going on. There's a bar and a pretty good restaurant. The non-divers would probably want a car to go do stuff, which is not a bad idea anyway and it's not that far to SMB. They have hotel suites with a bit of a kitchenette, or cottage type accomodations away from the water. The dive boats don't leave from the hotel often but they drive you not far to whatever dock they're leaving from. You can shore dive from the hotel as long as conditions are ok, or at their nearby shop at Turtle Reef which is a great shore dive.
On Seven Mile Beach where most places are, since it doesn't matter as much for diving it all depends what you want. Condo (a kitchen is a good thing) or hotel, how much you want to spend, do you want to be in the middle of the zoo/closer to town - or in a quiet area and drive to it? You could stay in a condo towards the north end of the beach like the Aqua Bay Club mentioned (I've heard that's quite nice) and be in a somewhat quieter area, but not have too far to travel to stuff and it would be fairly convienient to get a package with Divetech and use their shore diving facilities.
