I've been to Cozumel about 10 times... I stayed at Casa Del Mar 5-6x, El Cid 1x, the Allegro 2x, and most recently secrets 1x...
I did not enjoy El Cid, because of the tiny little elevators...
Casa Del Mar has always been a wonderful place to stay but I have not been there in quite some time...
The Allegro was decent, the food was meh... But the location was fantastic especially for a short boat ride to the reef... You would need a car if you stayed down there because the cab rides are expensive to town if you decide to go
Most recently, I stayed at secrets... I would never stay there again because it is not catering towards the divers... More towards vacationers... That being said there is not a rinse tank anywhere near the dock, and there are no lockers... It was a whole lot of fun carrying my gear all the way back to the room every single day without it being rinsed...
So I guess you're going to have to decide whether you're going on a dive trip or you're going on a vacation... I dove for 5 days in a row and it got really old carrying my stuff to the dock and back
Something else to think about, is going to an all inclusive in Cozumel kind of shot changes you because the restaurants are so good all over the island... There's no food on any all inclusive on Cozumel that can compare to the restaurants that you have to choose from
Hope that helps