We flew with Delta in 2004 from Gatwick via Atlanta to Orlando, on a Boeing 777. Check in was excellent - we were pulled out of line for a bag search and then ushered to the front of the business check in, even though we were economy - lovely! Seats onboard were fine, seat back entertainment great, service attentive, kids didn't complain once! Stop off in Atlanta was long enough for refreshments and stretch of the legs. We were a bit worried about Atlanta Hartsfield being so large but Delta's flight connection area was well signposted and simple to find - we claimed our bags and dropped them at the connection area within about 2 minutes of each desk - completely stress free.
Onward flight to Orlando took about an hour and was just fine...all in all no problems. We'd booked on Expedia so even got the seats we chose on all flights.
Just booked for March 2007 and would've used Delta but BA's current deal was too good to pass up
Enjoy!