Google Earth, Sketchup, Global Mapper - best way to generate terrain

Hello everyone. I’m trying to generate some terrain for my game. It’s an open water/island hopping game and I wanted to generate a heightmap of the Carribean to use. I have Google Earth, Sketchup, and took a brief look at Global Mapper (haven’t bought it yet, just used it at a friend’s). What’s the best way to generate terrain from satellite data?

Maybe “SAT DAT SPLAT” is something you can use(I´ve not tested it).