Second a lot of the thoughts above. If you want it (mostly) in English, Belize is your place. If you're looking to slow down, and just let life be calm, Belize again.
Guatemala is a great mix of so many things, it's one of my favorite countries in the whole world.
I enjoyed Nicaragua and would also agree if the urban experience is what you crave, Panama is not only easy to get to and earn United miles in the process, it's a pretty fascinating urban space!