i'm a Minidisc fan myself, but in terms of MP3 players, i like the iPod for hard drive-based players, and iRiver's iFP-195T for flash-based players. i like the simplicity of the iPod, and the newer models are very slim and easily PC compatible. The headphone amp is also more powerful than the originals. The iRiver is simply one of the best MP3 players i've ever used. It's got 512MB of onboard memory (you can't add anymore), an insanely detailed menu system, voice recording, etc. i didn't use the built-in FM tuner (or FM recording capabilities) much, but it seemed to work pretty well. It's not super cheap at roughly $300, but it's debatably the best flash unit to date.
Battery life seems to be an issue with MP3 players across the board -- one of the reason's i stick with MDs.