Hi Christina, I got a deal at Club Med (just a little down the road from the Sands), so I tried diving with them on the first day, as long as I was there. They were cheaper than the offsite operators, and they had a very nice boat that wasn't at all crowded when we were there last week, but they were staying pretty close to Grace Bay. Also, their surface intervals were so short, I was surprised to notice I was going into deco on the second dive. And they didn't have Nitrox available. It wasn't bad for a shakeout dive, and we saw sharks on the second tank, but the coral wasn't all that nice, and the sites they took us to looked kind of beat up. The vis wasn't all that great either, but that might have been the fault of a storm a few days earlier. On the plus side, both dives ended up being about an hour, even though they said the second dive would only be 40 or 45 minutes.
Caicos Adventures does West Caicos sites, which I thought were much better. Healthy, good-looking walls with lots of life on them (including multiple shark passes on every dive), and really good visibility. One of the CA divemasters was a former resort-op guy, and he said that the Grace Bay sites have been over-dove, and the coral is in bad shape largely because of careless divers.
We got to know a group that was diving with Dive Provo, and they were happy with them, too. Plus they saw a manta ray.