I'd probably go for the D600. Was playing with my mate's today and it's really nice, simple to use and seems solid.
I've got a Sony Ericsson K750i, pretty much the same as the W800 and i love it but i've heard soooooo many problems with the little stick going kaput. It hasn't happened to mine yet but did on my K700 and when it goes the phone is pretty much useless