Quote:

simplest, least expensive product to play back MP3s - with a decent sized screen



...quite often, you get what you pay for...

The advice for playing .wav over .mp3 for sound quality is good, sound (pun intended : ) advice.

But I think convenience is king, and carrying around the library in your pocket is really convenient. I would say your best bet for usability, quality, price, and small size would be the iPod touch - the more capacity the better (depending on your needs).

http://store.apple.com/us/browse/home/shop_ipod/family/ipod_touch

But it is rather pricey - 299 to 399.

So - just for you, at no extra cost, I googled "best alternatives to iPod touch".

Here's one of the first hits:

http://www.t3.com/features/best-mp3-players-to-buy

There is plenty of advice on how to get a good mp3 player for less money.

As far as the best bang for the buck in the laptop or tablet world, I'm not sure, but would be interested in other peoples' hardware suggestions in that area.