Are you already certified to some level? I suspect not as you've mentioned the OW and AOW courses. If not, it might be pertinent to know if you intend to get certified at home, do a "referral" in Cozumel, or if you intend to do the entire course while you're in Cozumel. For instance, if you're doing the entire course on island, whether or not the confined water dives are conducted in the ocean or in a swimming pool could factor into your decision. Another factor could be the number of people doing certifications. Is it just you? Is it a group of people?
There are many great instructors on the island. The details of your plans and expectations would help narrow down the list. Where are you staying or what kind of place would you like to stay? If you are doing the OW cert, does it matter to you if all 4 open water dives are shore dives? With some operations, that is the case, with others, 2 are shore dives and 2 are boat dives. (This factored into my decision when choosing the op that did my ow dives.)
Sandro and Allen at Deep Blue, are both excellent instructors, but if your heart is set on staying at Villa Aldora, it would make more sense for you to do your instruction with them. Same with Blue Angel, Scuba Club, etc.