I don't know much about the Atrix, but I'm sure it doesn't have the Super AMOLED + screen.
In my opinion, this screen alone makes it excel above many others instantly. I actually prefer the Galaxy SII size (4.3") because I think that's the sweet-spot as far as having a large enough screen but still having good pixel density (along with, in my opinion, the most important point about ergonomics - you can still comfortably do everything with one hand).
However, I got used to the 4.5" screen on the Infuse and while I would still go with the Galaxy SII any day if someone offered to swap, I am very much content with this phone. I was a bit upset on how late the GB update was coming, but from the sound of it, it's for sure to be coming in the next few weeks.
*Edit*
So I looked up the Atrix, and it looks like a dual core phone. I still think the Infuse was a great choice, but out of curiosity, what made you ultimately pick the Infuse?