I've been doing a lot of reading to replace my dying Clip over the past few weeks... The only ones of these I've used are A17 walkman and Clip+ and Clip Zip. I've briefly handled the old Cowon M2 as well (plenue D is pretty similar, though much nicer looking).
An oversimplified breakdown based on reading I've been doing the past few weeks:
- pricy, small, for ease-of-use, product finish/build quality, battery life, not the best specs: probably A10/20 Walkmen, Cowon M2 or Plenue D.
- pricy bigger, better specs, good functionality, but step down in battery life and UI: iBasso DX series, Fiio Xii series, maybe Shanling M2
- cheap, but good specs, mixed bag everything else: AP100, xduoo x3
- cheap, tiny, good-enough specs for a lot of headphones: Sansa Clip/Zip, Fiio M3
- rockbox!: iBasso(???) & Clip/Zip
I have an A17 Walkman and quite like it- it will read playlists but you cannot create them, except to 'bookmark' songs (it has five bookmark banks, each allows 100 songs), which is my biggest gripe... not the greatest specs either. I've been following the Plenue D thread and the few people with it seem pretty happy (and it just got a firmware update to fix some interface lag issues).
The best thing about the Clips, other than being tiny,cheap, having that awesome clip, and good enough for most portable headphones, is you can add Rockbox, which has playlist creation and a TON of other functionality... there's a bit of a learning curve but it's great. I belive the iBasso players have unstable builds of rockbox as well.
Another note about the clips (and older players in general, oddly sometimes newer players too) is they don't always support large capacity microSD cards... you can often get the 64 gig cards to work with them using a special formatting tool, though.