this is an old topic among pc/audio fi users, so i googled but couldn't find satisfactory posts.
the audio sources which i'll convert are usual 16bit audio CDs.
some recommend m4a(that of vbr 256kbps is generally ripped and being presented by apple) because it is made with the advanced codec that released later than lame and its 256k vbr can be fluctuated over 320k without unstableness.
others recommed mp3 320k cbr because mp3 is the most compatible format for tons of devices and usual people cannot tell the difference of sound quality if its bit rate is over 192k, adding i don't need to be possessed by ghost sound - socalled placebo effect - and bit rate number pointless.
actually many CDs ripped about 1~2 decades ago are largely converted to mp3 192k cbr and still in circulation. and nowadays no one talks about m4a's compatibility.
of course, uncompressed wav or losslessly compressed flac, tak, ape is the best, but they consume more mobile devices' battery and take up much memory.
i heard of the fact that audio systems with high quality external assistive devices and output units can easily tell the differences.
of the two, m4a 256k vbr vs mp3 320k cbr, anyway which is actually better format when i convert them with mc21?