You can probably get the exact % online, but roughly from my own collection, per album:
-> Actual CD (~600-700MB)
-> lossless about 1/2 of that (~250-300MB) (all in the same ballpark (ALAC, FLAC etc.))
-> MP3 highest quality under 1/2 of that (~90-120MB) (CB 320 takes a bit more space than VBR 0)
Of course it varies based on the length of the album and the complexity of the music... I have some lossless compressed album that are still over 420MB for example.
Personally, if I use lossy compression at all, I prefer VBR 0 since it delivers the same quality as CB 320 but cuts out the filler so to speak. Which is not an exact definition, but the real-world benefit is for portable use: I can fit a larger selection of albums. And without wanting to go down another codec debate, if CB320 vs. lossless can be tough depending on the music, I think an honest ABX of CB320 vs. VBR0 for the same track would be close to impossible to discern in any genre, at least when encoded with the most up-to-date version of LAME. I have certainly tried my hardest on a pretty decent setup, and really couldn't for the life of me even with tracks I'm very familiar with, so it does the trick for me at least.