JPEG's are fine for the final output.  If you are a purist you could output TIFF so everything is lossless or even 16 bit TIFF if you want the absolute best gradations in your prints but I don't think the difference would be noticeable on 99.9% of shots.

The main thing to note when exporting to Qimage is to leave the image resolution original (don't resample or change pixel size/dimensions).  Let Qimage do all the resampling because you want to do that at print time when you know the size of the print(s) you want to make.  When exporting, Adobe RGB color space is fine as well.  The only time you would need a huge color space like ProPhoto RGB would be when you have seriously saturated colors that test the gamut of your printer/inks and you use 16 bit (per channel) TIFFs as above.

Regards,
Mike