NEF or DNG RAW files for archiving?

Thanks for all of your feedback.  It sounds like the consensus is to keep the original NEF file so you have all of the data and don't lose some Nikon specific data.  I am going to work on my filing system and start saving the original NEF files.  Now I have got to decide if I want to save all of those pesky Sidecar files, or just save the original NEF's.  Decisions, decisions!!!