None of those 4 are more efficient than the other... but those are not MP3 files. I'm not sure how he defines quality of MP3s - could be referring to the sound itself and the quality of those sounds (ie. 44KHz vs. 22KHz etc.), or just how "good" it sounds compared to for example midi.. in that case, the 4 formats Axel mentioned should be used. Which one of those 4 are used really depends on what program the music maker makes the music with.