i got myself a w850i. I bought it becuase of its features mainly, if i were you i'd be asking myself what features you are looking for.
w850i has:
1gb memory stick
decent music player (playlists, organise by album artist etc.)
average video and camera (2mp - can print standard size photos well)
and the usual features you get from a sony ericsson
good sized screen + sliding thingy
pretty crappy buttons but you get used to them
btw i've used 2 nokia, 2 sony erricson's a motorola and a samsung phone before, so i know my phones ^^