If you live in the Atlanta area, or depart from the Atlanta airport, nothing beats the Delta flight, non-stop to Cozumel. The flight leaves 11-ish in the morning, and arrives in Cozumel about 2.5 hours later. This is perfect timing to arrive in time to check in to your choice of residence, and be drinking margaritas that afternoon. We live ~ 1.5 hours from the airport so we can wake up at a very normal hour on the day of departure if we are flying Delta.
While I agree American Airlines first class service is better (as long as you have your own means to watch a movie on the flight (no screen on the seat-back in front of you)), having to stop in Miami or Dallas more than doubles the travel time. And that typically means we're having to wake up about 3 or 4 am.
Delta, I know you're not following this post, but hear me...please keep your flights into CZM year round.