Your two airport options are LIR on the west coast and SJO (San Jose) in the big city and more center of the country. I've never flown into SJO so I can't speak to that experience but I certainly know it's bigger and busier than LIR. We live a half hour from LIR so we fly into there. More often than not, but not always, you can find cheaper tix into SJO. If your budget is a big deal you may want to choose an airport based on ticket prices. If budget isn't a huge deal, you may want to choose an airport based on what areas you decide to visit.
As the primary gateway to Costa Rica's enchanting landscapes and adventures, SJO connects you to both the urban charm of San José and the natural beauty surrounding it. Official site.
Positioned amidst pristine beaches and lush national parks, LIR is your direct route to a tranquil and luxurious Costa Rican vacation. Official site.