There are some great operations in Cozumel.
Some consecrations;
1. Go with an operation that limits the number of divers per Dive Master.
2. Check to see if they will pick you up at the Hotel, or Hotel pier.
3. Search the internet, basic search, scubaboard, tripadvisor, scubaadvisor.
In general, pricing will be fairly close. When you do research you will find people that both “love” and “hate” a given operation.
When the wife and I go to Cozumel we only stay at the Fiesta Americana and only dive with Chucho Divers, we have tried others (both hotels and operations) and have decided only use these.