mp3-mp4 is fine to me and sounds great where ever they are played :)
But then again I'm not listening to opera either ;)
Cheers.

With most compression stuff there's always the possibility of corruption is the only issue I can see,
For myself space is not an issue I prefer to leave files in a original state on what ever device...

I'm never really happy when something messes with files for no other reason than to save space when space is not an issue,
Cheers.