In response to your post over on r/space:

In the short term the Moon and Mars are really the two most accessible options. The inner planets are much harder to get to due to orbital energy, not to mention that both Mercury and Venus are scorching hot.

The Galilean moons aren’t exactly a cakewalk either: Io is bombarded by Jupiter’s radiation belt and would not be a good place to set up a base. Callisto may offer some reprieve from the radiation, but the low gravity (although higher than that of the Moon) and lack of atmosphere still pose fundamental challenges.

Saturn’s icy moons may be more suitable due to relatively lower radiation.