I'm in early stages of planning our first trip to Costa Rica for 2015. A family, the youngest will be 11, used to hiking and roadtrips, don't care about night life/restaurants or entertainment parks. Main goal will be seeing wildlife in natural environment, but we will probably include a coffee tour, a beach for a couple of days.
If it were sunny year round :), I would do this in July-Aug (two weeks trip): fly into SJO, do a 3 days/2nights trip to Tortuguero for the turtles, then spend a couple days in the Arenal area, then another couple days in Monteverde hiking the reserves, then move south to Puerto Jimenez for a 3 days/2 nights tour to Corcovado NP. Split the drive by spending a day in Uvita and the drive back in Manuel Antonio, or reverse. What I'm afraid of, even after reading quite a few trip reports about summer travel: 1. how much possible is it that in two days we won't have a chance to see Arenal volcano because of the rain? 2. bigger concern: It will be raining the whole time in Monteverde and we won't be able to see any birds. 3. To be caught in a heavy rain in the car, I understand the rain will be different than what we have here in New England.
Other options: use school vacation, go around April 20, or mid-February. That would be for one week or 8 days, and probably only for Arenal-Monteverde-Manuel Antonio(Uvita). Then some other time to Tortuguero-Corcovado. So here is the question: would you keep fingers crossed about the rain and go for July, or would you take 2 separate 1-week trips?
If the collective choice is Feb, I would have to buy plane tickets soon...