Cozumel? Cancun? or Playa Del Carmen?

I have been to all three here is my take Cancun party scene for 18-21 year olds beach is great. Playa great party scene as well but up to 40 somethings 5th avenue shoppimg nice ferry over to cozumel fun. Cozumel also Great beachs at resorts small snorkeling AWESOME parties better during day when cruise ships come in I like Cozumel best I am 45. It all depends on your age I like the laid back hang out thing. If you take a taxi further up the coast of cozumel you can walk the beach. all have the blue blue water PV YUK!!! So depending on your age that is how I would choose:)

I have been to Cozumel, Cancun, and Playa del Carmen several times. When you cruise, most often you visit any or all of the places you have listed, mostly Cozumel. Getting between Cozumel and Cancun, on a ferry, is a 40 minute boatride over not so smooth waters. Make sure to take a Bonine (motion sickness tablet 4-6 hours before taking the ferry). Party groups travelling from the USA often visit Cancun.

Puerto Vallarta.

I know...other coast. Way nice, and not quite as pricey.

I stayed in a nice little hotel called Playa los Arcos...really neat (a bit run-down, but more personable than the big box places).

I can't advise on your three choices,but don't agree with Puerto Vallarta. We went there in May and absolutely hated it. The beach and ocean were disgustingly dirty. I would hate for you to be as disappointed as we were.