Both devices come with fairly grim little screens, but the Sony's is by a country mile the grimmest of the two. The colour scheme looks washed out, the text is spindly, it's only three lines tall and at around 18 x 7mm it looks about 4mm too short for the space it occupies.

The Sony's display is the poorest of the two
The U4's screen is not only bigger - at 20 x 13mm, but also has a higher resolution – a whopping 128 x 64 - and can display four lines of text. It's easier to read than the Sony, nicer to look at and even displays little album cover images.
The “selling point” with both these players is that you don't need a separate USB cable. The U4 has a retractable USB plug - just push the release slider up and out it pops - while Sony makes do with a fixed plug covered by a cap.
Since said cap doesn't have a lanyard, we suspect it will quickly get lost, and while you won't be able to lose anything off the Samsung, the retractable USB connector isn't the most robust thing we've ever come across. If you suffer a case of unintended extension in your pocket, we suspect things may go snap.

Extra audio format support on the Samsung
Neither device is exactly bulging at the seams with audio codec support. Sony gives you MP3 and WMA, while Samsung adds Ogg to those two formats.
Both players come with FM radios and while neither have RDS, both let you assign up to 30 presets stations. Both players will also let you record radio content off air and come with a built in microphone for speech recording. The Samsung records in MP3 format, the Sony in WAV.
COMMENTS
->Soruk
I use a Creative Zen and ran into the Linux - MTP dubious friendship thing a few years back, since then Amarok (KDE App, should be available for your distro) has added full MTP support and is by far the best app that I have found for transfering to MTP / USB / Ipods
go for one of the 1.4 versions as they are currently working on 2.x and media transfers are supposed to be a bit cagy
SD memory based MP3 players
What happened to the MP3 players that used SD cards as their memory? I bought one from Micro Direct about four years ago for just £15. Now that you can get a 2GB card for under a fiver you can easily do this on the cheap. My player also had a little LCD to show the track name.
Chav-o-rama
What is it with El-Reg these days, taken over by cheapskate chavs? The Sony is a better sounding player, and costs a few quid more. Sound quality is a primary factor, so why did the Samsung win out? Because it's cheap tat.
If you want quality, you have to pay for it. I for one don't buy TV's from supermarkets, I certainly wouldn't touch a Xbox either as that's also cheap tat.
So what happened to all the large capacity players?
Most of the old HDD iPods have been shelved and everyone else seems to be flooding the market with 2-4GB models.
What's the best modern player for the music lover that wants to carry their entire (50GB+) collection with them?
(Extra points for it not being apple, as the latest generations of apple stuff are not Linux friendly)
More on Linux compatibility
Just because a device might be MTP and not Mass Storage doesn't necessarily mean it's not compatible with Linux. Case in point, my Creative Zen X-Fi works a treat with "gnomad2" using libmtp. This could be something you folks at El Reg could include in your tests.
