I was going through the same debate...read these threads
Sandisk Fuze vs. Sony Walkmans- sq only?
D2 vs Fuze..
Then threads contrasting the d2 vs the sony.
From what I've read:
Sony has a warmer sound signature (boosted bass)
Fuze is more detailed with a more flat sound sig
Sony has better eq settings (but not as good as cowon players)
Both have similar soundstage
Fuze is better for hiss
Both are basically very very good players.
I chose the fuze b/c its MUCH cheaper (by $70CND) with expandable memory. Although the sony does come with better buds I have a pair of SA6 that I just got today =) That and I perfer more details to more bass as I feel you can get more bass oriented headphones for that =)