I used Delta to the USA numerous times last year in Comfort Economy. I thought it was a £50 upgrade each way per person, so for a few more inches legroom I was okay with it.
As for Atlanta, nothing would get me back there. Unless it's since changed, horrible immigration officers, apalling/no queue management, security checks/strip-down before you can leave the arrivals area and it takes an age to travel from the terminal to the main building on the noddy train. Atlanta is the worst airport I've used in the USA.