MP4 is the "video" layer... MP3 is an "audio" layer.... (just in case you didn't know that)
I have no clue which player has the best audio output.... I would expect them to all be about the same quality.
If you are looking for super quality output, I would expect you will need an highr end external DAC.
I always hated Apple as well for years. At 1st the software is a PITA, but the hardware more than makes up for it !!!
TRUST ME, I was hardcore staying away from Apple products for 10 years... Now, I am even thinking about buying the 24" iMac... I have always liked Microsoft, and thought they were doing a great job, till Vista came out...
I played with Gary's Zune at CF... it was cool, but side by side, I'd still stick with an iPod. The interface on the Zune was a little clumbsy... the iPod wheel works way better than the clicky buttons on the Zune, and the iPod Touch, well, that's even more kick ass.
Think Storage... forget about who makes what, and what software you will be using. You'll only use the soft ware once a month, if that. Ipod and Zune are the only 2 huge players. Zune has a 40 and an 80 GB, iPods are 40, 80 and 160 GB.... I am a total tech geek, and I say get an iPod.
Get a used one, and play with it, if you REALLY hate, it sell it and get your $$ back, and buy the Zune.
Once you get used to iTunes, you will change your mind.
Just so you know, I have about 45 GB of music, and I have never spent 1 penny on iTunes.
Well, here's a list of the MP3's I've had.
Rio Carbon: $175 5 or 6 GB
This was probably my favorite player as far as looks go.
They are discontinued (bought out by apple and shut down) and are pretty fragile (don't drop it even once)

MobiBlu: $100 1-4GB
These are "cute" really small and work very well. Pretty durable.
The headphone really suck, and are built into the neck strap, so it's really hard to find anything to replace them.
Just checked their website, and they have a ton of new toys... AND it looks like apple bought them up as well
http://www.mobibluamerica.com/
iPod Shuffle: $75 1-2 GB
This thing is probably the one I use the most... it's STUPID small, and clips on to my shirt pocket.
I use it with a set of BOSE ear plugs and it sounds really good. I change my music out on it all the time, cause I can't put all 45 GB on there...

iPod Classic $150-350 80-160 GB
This one was great, it held EVERYTHING !! That's all I took to CarverFest 07' was an iPod... you can ask Tom it sounded GOOD for being poor MP3 formats. BIG STORAGE for lossless files !!!!

iPod Touch 8-32 GB $200-450
I like the screen on this one the best... Big ass touch screen for watching videos. WiFi, YouTube, AIM, Calc,
Pretty much an all-in-one media player. The biggest downfall to this one is the price... this one ain't cheap.
But you ARE getting what you pay for in this one !!

When it comes to Tech Toys, Apple really has their shit together, and are leading the race by far, and winning.
Microsoft is about 6 months to a year behind them, and always trying to play catch up with them.
I used to be SOOOO ANTI-MAC.... now... I am slowly going over to the Dark Side... as where any Mac user will say...
No.. You are finally starting to see the Light....
Either way... STORAGE STORAGE STORAGE !!!! Get something BIG !!! It will go FAST.........