Been a while, so some things may have changed significantly and there’s probably a bit more tourist infrastructure than when I was there 15 years ago.
Where in Central America are you arriving and how long are you going for?
If you’re after beaches, the Pacific tends to be warmer and Costa Rica tends to have the best beaches (the name kinda gives it away); taking a trip down to Corcovado National Park and stopping off at Uvita on the way comes highly recommended. Watch out for shady characters in Golfito.
Isla de Ometepe in Nicaragua is well worth a visit if you like massive freshwater lakes full of sharks and climbing volcanoes
Guatemala has the best overall blend of natural beauty, culture and accessibility; Lake Atitlan with its towering volcanoes, Tikal with it’s sprawling jungle ruins, hiking the highlands around Todos Santos Cuchumatan and the chilled vibes of Lanquin with caves, natural hot springs and tubing down the river in the twilight as bats flood out of the caves
Unless smoking crack and getting stabbed are the kind of thing you’re after, avoid Colon in Panama
I could go on…