I use gimp occasionally as well as CorelDraw.
Our typesetter uses Photoshop.
The impression I get from speaking to the typesetter, is that Photoshop has an easier interface and generally easier to use with a few extra features. Photoshop does have a nice extract filter that gimp doesn't.
It is more important to understand the techniques used by the software, than to have the cutting edge software. It does take a bit of trial and error.
In Photoshop, our typesetter says there are 3 ways that he uses:
1) Clipping path - Rarely used, but often chosen by the inexperienced. This gives a hard edge, but he often gets round this by adding light to the edge to break the sharpness.
2) Airbrush the background - He would normally add a bit of noise to the filter of the airbrush to make it look less perfect.
3) Use the extract filter - most common.
In Gimp I see 2 very similar options for the first 2, but there is no extract filter
Below I have found a tutorial that helps compare the 2.