If you're archiving, archive in Flac. You'll save space and can ensure that you can encode it to mp3 or burn as wav without losing data or residual artifacts.
If you save as mp3, decompressing and recompressing will eventually lead to signal noise and icky stuff.
If you save as wav, you won't have the tags and metadata. And you'll be wasting space.
I really think long-term data backup should just be in flac. I rarely need to encode to mp3 these days, it's not really a bother when i to need to...