Progresso is not the best port IMHO. Look at it on Google maps and it will give you an idea of this port. The ship docks about 5 mi. out on this very long pier. They have buses that take you into Progresso for free. In progresso there are beaches, but the water is usually murky. We went on a tour into Merida. It was just OK. You can still hang out at the beach, and have a good time, just not great snokeling.
I am sure there is someone else here with more info. Enjoy what ever you do.