We have flown into Liberia on our last couple of trips. I like the San Jose airport more. It is more modern and full service, and I always enjoy visiting with our San Jose hotel friends.
But the drive to Monteverde from Liberia is an hour shorter. While American Airlines is absolutely my least favorite carrier, they have a flight to Liberia that goes through Dallas. This allows us to avoid the headaches of the Miami airport.
We drove up the road through Las Juntas. This is the first time we have gone this way, and it is the best road that we have found yet. There is a very good paved road from the Pan American highway that leads into Los Juntas. You have to navigate a little in town, but if you can find the statue of several Campesinos, you are on the right track. Turn here, and you are on the road to Santa Elena. There is good paved road leading out of town, and only the last twenty kilometers (twelve miles) are unpaved. Even then, this road is in very good condition and is generally not as scary as the other road up from the Pan Am. It probably is not worth the extra drive from San Jose. But if you are coming from Liberia, this is by far the best choice.