Well, all portable device has its good and evil. You just have to get the ones that suits you the most.
I will give you the reason I pick iPod.
GUI and ease of use
Very freaking simple GUI, the click wheel is just genius.
Awesome Sound Quality
Its sound quality can be the best if get a pocketdock / sik ram din + amp. When people talk about sound quality, they usually refer to the sound quality from the headphone Jack, but they forgot with iPod you can get the sound output from the bottom connector as well, and the sound from it is terrific.
Accessory
Just look around how many accessory is available for iPod.
Evil Stuff about iPod
Sound Quality
the sound from the lineout Jack has problem work with low impedence headphones. For example, the very famous bass roll off problem. Also, with any iPod Photo, there is distortion on the music and it is quite noticeble.
None-replaceble Battery
This is just pure evil. means I will have to replace my ipod after few years of use.
Tight integration with iTune Music store
LOL. I want to buy songs from napster, but I am screwed because iPod only works with iTune music store period.
Therefore, as you can see, there is no best mp3 player yet. You have to pick the one that suits you the most.
As a final comments, if all you care is sound quality, get ipod because only with iPod you can get the best sound quality, but you have to use pocketdock / sik ram din + amp.
Its sound quality is not that good through phone jack.