My early diving experiences were in Cancun. Used to go there with my ex and her family. I actually got certified in Cancun. But it was definitely not a dive vacation. It was a beach vacation with a little diving. Reefhound has it right. It’s pretty fishy, but the coral formations don’t compare to Cozumel. Overall, it’s not bad diving. But Cozumel is great diving. I’ve been to Cozumel about 20 times now and have already booked my next trip. It’s definitely worthwhile. No one from Cancun will take you to Cozumel. I know the shops in Cancun advertise Cozumel diving (or did, when I went there), but that means they will arrange for you to take the ferry from Playa Del Carmen and meet some other dive shop in Coz. I did that once from Cancun. It was a long and frantic day. I don’t advise it unless there are no other alternatives. I did the bag drag in July. In the winter I can get a nonstop into Cozumel from Detroit. The bag drag is really not too bad, but I would have to save a lot of money to do it again. I understand it’s not easy to get to Cozumel from LA, so if you can fly nonstop into Cancun, the bag drag probably makes sense. In Cozumel, I like Aldora for big tanks, long bottom times, the great staff, and their efforts to group divers of similar experience and ability together. I stay at Villa Aldora. It’s very reasonable, very nice, and makes a good combo with the diving.
If you have a short trip and have doubts about doing the bag drag, diving from Cancun is not a bad alternative. It would certainly be less tiring that going to Cozumel for the day.