I haven't used either in quite a while (though I was an early beta tester for World Machine years ago), but as far as I know they still break down in a similar way:
World Machine is largely procedural and node-based, similar to Terragen 2. You generally don't use it to create super explicit terrain forms (e.g. "painting" a mountain), but rather you create realistic terrain procedurally that looks like you want it to look, but is not necessarily an exact shape. You can create paths, guides, etc. to control the shape, but it's still not the same as painting explicit shapes.
Geoocontrol is more of a terrain "painting" app, intending to give more direct control and feedback, but it does seem to have less procedural power and pro-type features in general (e.g. tiled terrain, 8k terrains, etc.). Geocontrol does have very nice river tools and general erosion.
Which you prefer will then depend, I think, largely on what interface approach you prefer. If you like TG2's node-based UI and "node graph" data flow approach to creating, then World Machine may be for you. If you prefer a more explicit, direct, "painterly" approach, Geocontrol is probably more your speed. Which terrain output you prefer is, I think, a personal preference. I find both WM and GC to have realistic and beautiful terrain output in the right hands.
- Oshyan
