I've been to Cozumel several times and if you are a beach person looking for a place to just soak up the rays my pick is San Fransisco Beach. There are lots of water sports available if you some activities. They have a small resturant/bar, with waiter coming out on the beach to serve you. The Pina Coladas are great. It is a short taxi ride from the pier.
We did the ECO JEEP excursion and it was awesome too! Lots of laughs. There is a new one called RACE FANTASTIQUE which sounds incredable. We're gonna do it the next time we're there. And like Dave says, DO NOT MISS Pancho's Back Yard! Great Margaritas with a coupon available on line. And the food is unbelievable. The best gazpacho in the world!!