I've got both an 850 and a 900 and I prefer the 900. I think it looks better and feels better in the hand.
It's taken a little bit of a different approach to make do with the different buttons but I like it alot. Both are a compromise so I'd rather the one that looks and feels better and I'll work through the missing buttons.
I kind of wish you could get replacement buttons for the "listen" and "watch" buttons, that way you could customize it more. Say, "favs", "shortcuts" "what to do" as well as the watch and listen. That would allow a little more customization while still having the hard buttons to direct you to major tasks. And a "back" function!