MP3, I'll be back in fashion when the hipsters ironically adopt it.
I'm fine with it as long as the compression is kept to a minimum. Hell, I still use Winamp Pro (on a Win7 partition as it won't see the CD drive on WINE in Linux Mint for some reason) with LAME set to VBR quality 0 and the bit rate from 32kbps to 320kbps and it works. Far smaller file sizes than FLAC and when listening on the move or with other noise around it sounds fine to my uneducated ears.
The thing we should really remember is CD is a 'compressed' format too - with arty farty facts as well. It's 'only' 16 bit and 44.1KHz, so a fair bit of the original sound of a performance has been lost. But that gets us onto the merits (or otherwise) of HD formats like 24bit 96KHz, etc, which will probably just end up with us all flaming each other...