Porque no las dos? [Translation: Why not both?]
What I mean by that is that I like FLAC, so that if I have to burn to CD for a friend, then I'm getting the original CD quality. Plus, as someone said, you can convert to any format required. I've been redownloading a lot of discographies that I previously only had in mp3.
That said, I've got an iPod Classic connected to an FM transmitter in my car, so mp3 is all I need for that purpose. Also, if it's something I'm not sure I'll like, I'll get the mp3 down first. If I like, then I'll look for FLAC, but if not, then why waste the time/space/effort?
As for vinyl rips/24 bit, well I'm only listening to music in my car on on my computer, so there's no need for these in my case.