Selfportrait and RAW handling

At the moment I use Canon’s EOSViewer Utillity and The GIMP for RAW handelling. While I need to figure out how to use The GIMP without getting heaps of artefacts/noise, I get quite often strange artefacts that are white curves that follow the light within a picture. To give an example, look at this selfportrait (not the best portrait as my eyes are crossing). The first picture is using The GIMP:

The second one is using Canon’s software and then cropping it slightly in Photoshop:

Any suggestions to how NOT to get these white curve-artefacts with Canon’s software? What kind of RAW handelling software do you prefer, and what do the pictures look like after you’ve exported them to jpeg?