MP3...
...is plenty good enough at 320kbps. Or even 200kbps VBR LAME. Like you say, it's widely compatible, and more to the point, storage is cheap so you can have good quality at the expense of slightly bigger files.
Personally though, I'd still rather have it in FLAC. It's not that I can hear the difference most of the time, it's just that I feel somehow cheated out of the bits they've thrown away...