Playa Espandilla (a lot of people call it Playa Manuel Antonio)/ Manuel Antonio, Costa Rica
During the summer months (let's say July to September) it is a good beach for surfing. On some days you can get waves up to 2,5m high, but the current is usually not that strong so it is not dangerous to swim. Try not to visit this place during October, as it is raining season (also refered to as "winter"). The sea will get very rough during this time of the year, only very few "brave" locals go surfing then, and most shops and restaurants close because tourism is at it's bay. Raining season also means that it is likely to rain for weeks none-stop and temperatures fall down to 25°C. Air humidity rises up to around 95%.
December is the busiest season in terms of tourism for Costa Rica, only followed by the weeks around the Easter holidays.
The sea gets a bit calmer around December, and the temperatures rise to around 35°C.
I like beaches that have a bit of infrastructure. You have a little market and a variety of restaurants at this beach, that allow you to take a break from the beach and the sun!!! and take a stroll around those little shops or a cold drink at a restaurant. There are different restaurants that serve different types of food in different price ranges, so there should be somthing for everyone.
The sunsets at the Pacific coast are some of the most beautiful. This picture does not even do them justice. The picture was taken from a restaurant that is famous for it's view over the bay. (El Avion) In my opinion, food is ok but what you pay for is the view (at least that was the case 2008 and still 2009).