AT&T must really love the iPhone as they keep releasing subpar Android devices that aren't giving the high end smartphone consumer much of a choice. AT&T was the last carrier to provide Android devices to consumers and has done it so far in a rather lackluster manner that shows me they are not very committed to supporting Android. The latest device, the Dell Aero is launching with Android 1.5 and I am sure still includes all the AT&T crapware and limited access to applications outside of the Android Market.
Other Android devices you can find on AT&T include the HTC Aria (the best of the bunch), Motorola Backflip (strange design and older OS), Samsung Captivate (nice hardware, but locked down a bit and poor overall performer with AT&T junk), and Sony Ericsson Xperia X10 (again Android 1.6 loaded at launch). We even see the smartphone/tablet device, the Dell Streak, launching with Android 1.6.
The HTC Aria is quite good with a bit limited processor speed compared to other high end devices and a lower resolution display, but it comes in at a good price and if it didn't have the AT&T lockdown and promise of an Android 2.1 or 2.2 update then it would probably be the one to buy. I thought the Samsung Captivate would be outstanding and even recommended it to a coworker who now comes to me every other day with issues and I have seen it locking up for no apparent reason. I also don't appreciate the lockdown AT&T puts on it and agree with much of what Jason Hiner wrote concerning the "openness" of the Android platform.
Other carriers add in their own stuff too, but in the case of Sprint, Verizon, and T-Mobile we have seen them including their own branded tab in the Android Market so the consumer has the choice in most cases about which apps and services they want to install and use. AT&T has always loaded their junk on most all of their smartphones with no ability to remove, but has left the iPhone alone.
If I was an AT&T customer, the choice for a smartphone would be easy and it would be the iPhone 4 all the way. I wouldn't consider an Android device until we see more openness by AT&T and I imagine that won't be happening anytime soon.