Calisto is a better location than Ganymede
I got it somewhere that Ganymede is within a major radiation emiting from Jupiter, as are Europa and Io, but Calisto is just outside that intense radiation zone. Then again, Ganymede has a magnetic field that might offer some protection from jovian radiation?? Anyone know the answer to that one?
But I would still think Calisto is the best bet for a human base in the jovian system.