For overland maps, the Gimp is vastly superior to CC3, in my opinion. Not that CC3 isn't useful, but it's a bit limited. For encounter-scale maps and cities, CC3 with its expansions is very quick and efficient, particularly if you pair it with Gimp or Photoshop for post-production work.

Do take a look around for what you can do with the free software before you drop any dough on other software. Then spend that money on a Wacom Bamboo Fun tablet instead!

Oh, and I would be remiss if I failed to mention that Fractal Mapper has a free trial, as does Dundjinni. Last I checked CC3 did not, but that may have changed. And Inkscape is an open source vector drawing program capable of the sort of graphics that Adobe Illustrator can make (though it is not yet nearly so robust as AI).