The products were released six years from each other. That's like three generations of technology apart, so you get into the question of whether it was best of its own time or best because it was just the most recent.

But I urge you to play around with a Zune HD sometime if you get a chance. I adore that UI because neither form or function were sacrificed, and both were excellent. I think my favorite UI element was a very basic one, in that it took me an equal amount of time to get to any artist in my collection. There's an extremely short example of how it did this here (it'll be over in about 4 seconds). It really amazes me that all other players simply present your collection as one giant list, and insist that you use a search to get your music. That's much slower than the method the Zune HD used (and I assume WP7 phones use it too).

Anyway, I just wish I could skin the Android music player. It's pretty bad. None of these mobile platforms have a good default music player, frankly...