I love Manuel Antonio beach! It is my favorite beach so far in Costa Rica, and believe me we have been checking them out. We even took our christmas card picture there this weekend. It was beautiful at the beach and we enjoyed teaching and just hanging out.
There are many beaches here in Costa Rica and we have checked out many.
We also like Puerto Viejo, which is on the Caribean side of the country. It is very laid back and a little bit more affordable.
On the Pacific side we have visited Jaco, Punteranus, Samara, as well as Osa Peninsula. We did not care for them as much as MA. They are a little more crowded and more expensive. There are as many beaches as places people are coming from to choose from though so there is lots to pick from. If you would like more info or help planning a vacation feel free to contact us, we love to share Costa Rica with all!