Cozumel's beaches come in two distinct varieties. The sheltered west coast, facing the mainland, has the calm clear water that drives the diving and the cruise-passenger snorkelling. The east coast, exposed to the open Caribbean, has long stretches of empty sand, dramatic surf, and almost no development at all. If you have a day, you can see both.
The best western beaches lie south of San Miguel, along the road to Punta Sur. Many are run as beach clubs charging an entry fee that includes loungers, food, and sometimes drinks: Paradise Beach and Mr Sancho's are popular, busy, and family-friendly. Playa Palancar, further south, has a quieter feel and good snorkelling from the shore.
The east coast is wilder and emptier. Playa San Martín and Punta Morena are wide open beaches with strong currents — swimming can be dangerous but there are usually a few rustic palapa bars selling fresh fish and beer. Currents on the east side make swimming risky except in a few sheltered coves; ask locally before getting in.
For a quick fix near town, Playa Azul, a few minutes north of San Miguel, has shaded palapas and lounge chairs at a moderate entry fee, and the snorkelling at Dzul-Ha at its southern end is decent.