Generally I use JPEG files for everything. But I shoot always shoot RAW with imbedded JPEGs so that I have the RAW files for archiving and fine printing. It may be hard to tell the difference between RAW and JPEG, and it would be a pain to do a really controlled test. But, with RAW files, you have the confidence of knowing that there's no compression and you're making the processing decisions. When it really counts, it's nice to have the RAW.