I tend to prefer non-all-inclusive as Cozumel has so many great restaurants. Perhaps you'll reconsider.
I've stayed at Palace (highend, close to town, all-inclusive, has spa, no beach but has house reef, should be wired for high-speed internet), Coral Princess (middle to highend, should be all-inclusive, has spa, small beach and house reef but very, very far from town), Caribe Blue (middle of the road, small not very good restaurant on site, small beach, a little farther from town than Palace) and Hotel Flamingo (Cheaper, has restaurant and great bar on site, has a computer for guest use (for fee) in town). I guess it depends on your budget, I have been very happy all all, although I won't return to Coral Princess due to distance (taxi is a must).
Bummer BlueXT (my favorite) is fully booked. If I were in similar shoes, I'd consider these, which have been well-regarded (there're are definitely more to this list, i just don't know them):
Liquid Blue
Deep Blue
Aldora
Do enjoy your trip (weather, diving, food and all). Dive safely.