Actually, the 810 is a bit better than the 820 if you consider the bigger battery and better FFC.
...... and Gorilla Glass! I also think the 810 looks nicer and the feel of the matte battery door is AWESOME! Also,the 810 doesn't pick up fingerprints while the 820 is a fingerprint magnet. I believe the 810 will work on AT&T's network since the phone does have the 1900MHz band support but it must be unlocked and I don't know how you would get an unlocked 810 this early after launch. Regardless I would wait until somebody else tries it on the AT&T network before purchasing. My 810 is perfect! I can't imagine carrying any other phone after having it.