The main beach, Playa Guayabitos–La Peñita, curves two miles north from the rocky Guayabitos [1] headland and point, growing wider and steeper at La Peñita. The shallow south-end Guayabitos cove, lined by palapa restaurants and dotted with boats, is a favorite of Mexican families on Sundays and holidays. They play in the one-foot surf, ride the boats, and eat barbecued fish. During the busy Christmas and Easter holidays, the beach can get a bit crowded and messy from the people, boats, and fishing.
Farther along toward La Peñita, the beach broadens and becomes much cleaner, with surf good for swimming, bodysurfing, and boogie boarding. Afternoon winds are often brisk enough for sailing and sailboarding, though you must bring your own equipment. Scuba and snorkeling are good, especially during the November–May dry season, near offshore Isla Islote [2], accessible via rental boat from Guayabitos. Local stores sell inexpensive but serviceable masks, snorkels, and fins.
A mile north of La Peñita, just past the palm-dotted headland, another long, inviting beach begins, offering good chances for surf fishing and beginning and intermediate surfing.
Links:
[1] http://www.moon.com/destinations/puerto-vallarta/the-nayarit-coast/rincon-de-guayabitos
[2] http://www.moon.com/destinations/puerto-vallarta/the-nayarit-coast/rincon-de-guayabitos/sights/isla-islote