I was in Aruba three weeks ago and have been to Cozumel three times. I'll go back to Coz, but probably not to Aruba. It's not that I didn't have nice dives in Aruba; I did, but the coral reefs in Cozumel are much more impressive. Aruba has the wrecks, but once you've done them, you've done them. My vote would be for Coz.