King & Spalding has a pretty terrible reputation. Their IP attys seem to enjoy their jobs, but most of the rest seem pretty miserable. It's as close as Atlanta really comes to a "white shoe" traditional firm, and they work their associates in a similar fashion to prove it. I think I know more people who USED to work at K&S than I do who work there.
A&B is pretty standard. People I've talked to from there seemed pretty nice. Their attorneys generally have a good reputation, and the firm puts out decent work product. I don't know really how happy they are.
Sutherland tries to put out a good word about themselves, but I've heard mixed things. I know someone who will be working there after they finish clerking, and that person was happy there. Quite a few people I've talked to said people are happy, etc., but then others say its a sweatshop with little professional support, etc.
Paul Hastings is one of the more international firms in Atlanta. People that I've met typically seem pretty happy, and they're known for their employment law practice. They have their share of attorneys leaving after a few years, and they do make demands on their time, etc.
The bottom line for all these firms is that some people click with some, and not with others. Atmospheres and inter-relationship are different. As "BIGLAW" (at least for Atlanta), they're all going to put demands on your time. Additionally, each practice group within a firm has different personalities and approaches - some partners may want you in the office if they're in the office; others may not care if you go home for dinner and then work at home for a bit, etc. They all work for a lot of the same clients, and do much of the same work, generally. Each firm has it's own "specialty," but they're all full-service. Paul Hastings may be more international, but that has a lot to do with the different route to expansion they took re: not focusing on the SE or buying up smaller firms in smaller markets, like Charlotte, NC.