The curved glass on the 800 definitely looks nicer, it's really one of the nicer parts of the design, I was a little disappointed when I saw it didn't make it to the 900.
However, I'd gladly sacrifice the curved glass for 4G LTE speed, a much more robust battery and the clear black SuperAMOLED+ screen. It's arguably the nicest screen on ANY phone right now between Samsung's SuperAMOLED+ and Nokia's clear black polarization. I've seen it side-by-side and the 900's screen has much deeper, richer color than the 800's screen. The curved glass is a minor cosmetic point as opposed to the other features which are functional.
That trade off makes the decision easy.
If Nokia could just find a way to keep the screen size the same and make the phone just a *little* shorter, by a 1/2 inch or so, it would be perfect.