There are 2 Sony Net MDs and a Sharp in our family. We still have MP3s..but there are no comparisson. The MD wins! The Sharp has a great battery system and I am able to listen uninterrupted for about 70 hrs on a rechargeable Lithium and single AA backpack.
The Sony software does have it's drawbacks in that any MP3 tracks that are converted to ATRAC for use, cannot be shared with any other MD players. There also is a limit to the number of times that the tracks that are stored on your HD can be converted, to and from ATRAC via the Sony software system. The only way around it is to keep downloading fresh MP3 files. Still cheaper than buying!