Never have, and it's totally on my bucket list. My folks went diving there back when it was still British Honduras, and it was quite rustic at the time...probably a bit more in the way of amenities nowadays.
Costa Rica's uniqueness arises from the crazy topography (essentially the entire American landmass compressed into 100 miles, where you can go from coast to coast over high mountains in a single day). Belize is pretty much all jungle from what I understand. But amazing coral reefs from the sounds of it, if one is into diving or snorkeling.
I feel old. I remember British Honduras ... Sun never sets and all that. Have a few friends who went to Belize and loved it. However, I like the topography aspect you mention with CR. I like changes of scenery/wildlife/weather/etc.
