Atrix.
1. Cameras: I'm sure they will both be quite usable, and the 5mp may be optically similar, or even better than the Bionics 8mp camera. It won't bother me if its not quite AS good, so long as its good.
2. Form factor: I prefer the 4" screen over the 4.3" screen, and the pixel density is higher on the Atrix (same resolution, smaller screen size).
3. Finger Print Scanner - I have been waiting for this on a phone for a long time. Not necessary, but just like on my laptops, I really think its nice to have.
4. Webtop application - this is the future of how most people will compute. I am excited, and can see myself using this whenever I travel and then some. This is the big one for me.
5. More RAM - 1GB vs 512MB. This won't be much of an issue for most people yet, but when we start using it like a laptop with the dock ect, it will definitely be something you will see a difference with.