I got myself a riovolt, because it was rated very good in all the tests I've read (click here for the the broadest comparison of such devices I've come across). The only drawback is that it's got no internal charger.

Contrary to what somebody said in this thread, the battery consumption is supposed to be much lower when playing MP3s than when playing audio CDs -- but I've got no experience, since I'm only on the second set of batteries right now; but it makes sense, as the biggest consumer would be the CD motor, and there's much less data to be transferred with MP3, so the CD is not turning most of the time.

Sound quality is good, there's a line out, no noise to be heard from the stereo even on quiet passages of audio CDs.

The quality of the included earphones is not that good, they're rather weak on the bass side, using the "superbass" setting on the built-in equalizer (which apparently only allows to boost [not attenuate] bass and treble; there's 5 presets and a user mode) helps some. They're also a bit quiet, especially when listening to quiet stuff on public transport. I didn't try other headphones yet, so I can't say if this is related to the player or the earphones).

Firmware is upgradeable by writing it to a CD-ROM (the stupid self-decompressing exe file it comes in must be run in DOS to extract it) and booting the player with it; takes about 30 seconds.

It works with all sort of bitrate MP3s (the worst stuff I have is 22kHz mono 24kbps) and VBRs as produced by lame.

It also has no problem reading cheap writeables or rewritables.

I like it.