I know this is a debatable point. The best beaches could be in Jaco, Tamarindo, Quepos or Puerto Viejo. But I didn't go to any of those places, so for me, the best beach was in Manuel Antonio National Park.
The reasons why are multiple. First off - as you can see, there aren't any other people in this photo. Because there weren't any other people on this beach. Manuel Antonio is a National Park, so you have to pay an entrance fee to get in. Therefore, there aren't a lot of people there. Pay the entrance fee, pack a lunch and stay for the day! But keep an eye on your belongings because these little guys are tricky:
And if this family doesn't eat your PB&J sandwich, guess who else is waiting in the wings to get their hands on it?
A beautiful white sand beach with raccoons and monkeys vying for your attention, but no other tourists in site? Sign me up!