I have a family plan with Tmobile and my children have androids and regular devices. I've used the G2 and I'm now trying the Atrix. My kids are staying with Tmo because it's cheaper, but I'm finding myself in areas where I don't have coverage and my kids need to reach me, so coverage wise, I have to consider ATT.
The G2 is a smoother running device (from an OS standpoint) than the Atrix, this may be due to the Motoblur overlay. With the G2 there are no lags, 4G speeds when you have it and excellent voice calling. The Atrix has been laggy; it freezes if you make a request too fast; I have to slow down to use it. Is this motoblur?? You just expect with the Tegra chip and blah blah blah, the device SHOULD NOT have this type of lag or freezing. The noise cancellation on the Atrix is solid, the stereo options are better than with the G2.
I find the Atrix browser to be a bit choppy at times, I did not experience that with the G2. Now is this the device or the network?
Now none of these are a deal breaker, but I gather the Atrix is a plus if you are into gaming or need to take advantage of their accessories to convert it to a netbook. The Atrix has a decent front facing camera; the G2 does not. The Atrix is more pocketable and has a slightly larger viewing window. They both have SWYPE.
With all the lag and freezing, I'd probably still opt for the Atrix over the G2. I think the Atrix is over priced, especially for the issues that have been uncovered with the WIFI. WIFI interrupts data connectivity. I've noticed that WIFI drops off a signal, which is annoying since you try to use WIFI to stay within your 2MB limit.
Once 4G is really ON with ATT, the Atrix might outshine the G2 in performance. The Atrix is very fast, when it's not freezing.
I hope I was a help.