I personally have never heard of the "wv" format you're talking about.
AIFF and WAV are at the top of the pyramid. Completely uncompressed and are also, the largest file size. Songs that are in this format are typically 35 - 40MB each depending on length. Not sure about AIFF, but I know that WAV doesn't support metadata.
ALAC, FLAC, APE, etc, are compressed lossless files. You can convert back and forth from AFF/WAV to any of these all day long and you won't loose any sound quality. You won't gain anything though either. Files sizes are about 12 - 18 MB each.
MP3, OGG, etc. These are lossy. Anything under 320KB/s is crap, IMHO. If you have these, it'll do you no good converting to any of the previously mentioned file types. Once the data is gone, it's gone.