I would strongly suggest Costa Rica. There is great diving in the Catalinas in Guanacaste and Isla Del Cano in Osa. Ther are also an incredible number of other really fun things to do. Below I have a small list of greta places and things to do.
Tabacon Hot Springs- a small river that is over 100F. Don't go for the cheaper places that are just swimming pools with hot volcanic water piped in.
Ziplines are every where, Hacienda Guachipelin has some with a "rappel" Tarzan swings and more.
White water tubing, also at Hacienda Guachipelin.
Wildlife viewing that is just amazing.
White water rafting.
Hiking to see active volcanoes, or mountains up to 12,500 ft.
Kayaking in rivers, flat or white water, or in the ocean.
My wife and I have been there ten of the past twelve years and will not tire of it. It is not the place to go for a dedicated dive trip, but if you want some great diving and a bunch of other fun stuff to choose from Costa Rica is going to be tough to beat.