Never dived Cayman, but I had always planned to use Divetech when I finally got there. Anything in particular that they did, or were you just looking to find something better?
My son and I have stayed at Cobalt Coast twice and dived with Divetech in 2007 and 2008.
Cobalt Coast is a very good hotel run by a very caring owner, Arie Barendrecht. The relatively isolated resort is in great shape and is very comfortable. The onsite dining is really superb and the meal plan is well worth the expense, even if you plan to take some of your meals offsite. There is free internet access in all rooms and public spaces.The place is very quiet and peaceful at night.
Divetech is a relatively large operation yet delivers very personal experience. They very reliably deliver 2 tank morning dives, generally on the North Wall or on the West Wall when this is not possible. Though they offer guided dives, they are more than glad to allow experienced divers to plan and execute their own dives. Dives are generally limited to an hour, more than enough time on the deep wall dives and/or the second moderate reef dives. Nitrox is readily available at modest cost for the duration. Divetech offers two shore diving sites at no cost to visitors, Cobalt Coast and Lighthouse Point. Both are superb shore diving sites. In addition, they offer numerous additional diving opportunities. They offer a great DPV dive, the West Bay Express in the afternoon between Cobalt Coast and Lighthouse Point that should not be missed. It covers terrain infrequently covered by most divers. They also offer a humbling CCR experience dive that should not be missed by anyone contemplating CCR diving. I must admit, I had neutral buoyancy for at least 15 minutes of an hour dive.
I would return to Cobalt Coast and dive with Divetech in a heartbeat. The only competition would be the opportunity to dive off the East End with Ocean Frontiers.
Full disclosure, I have 142 dives off Grand Cayman on 8 trips since 1997. If you're interested in additional afternoon or night dives in addition to what Divetech has to offer, I would consider booking with Renee Knight and Cayman Diving School, you won't be disappointed. Feel free to PM with questions.
Good diving, Craig