BEST is so subjective
We are NOT adventure people so zip lining is not on our bucket list
We did the Tortugero Canal Tour in CR from Port Limon
It was interesting & we did see a few animals but I think in mid day they are staying out of sight.
We stopped on the way to the banana plantation & some boys had a sloth ...you can get a photo of them holding it (for a fee of course)
pretty docile creatures.
We enjoyed the tour to the falls in Dominica.... very lush island
Tour to Antigua in Guatemala ...if you like historical buildings etc...it is a Unesco site