Hello from Atlanta! I've flown BA a few times out of here... and no, it's not particularly bad as a BA pax, but it's also not a great experience mainly because of the lounge.
BA's check in is at the International Terminal (F). To my knowledge, no hotel has shuttles directly there... so if you have to check luggage and are returning a car, staying in a hotel, or using MARTA, you will have to take a separate airport shuttle van that drives you all the way tot he other side of the airport. It's not the worst thing, but it's not a world class experience either. If you don't have to check luggage and you have your boarding passes, you can go directly to the domestic terminal and use whatever line (TSA Precheck, Clear, for common joe lanes) because all of the terminals are connected by a relatively efficient train.
BA's contracted lounge sucks. There is some food, but it's just not good. The lounge is generally overcrowded as it's also used by every other non-Delta/non-Skyteam airline as well as Priority Pass. Yet it's not particularly big. There are some very good restaurants in the airport. A favorite from the Delta side of things is One Flew South in terminal E. Ecco in terminal F is also good. Food at both are FAR BETTER than the lounge options.
Edited to add: AA has a lounge, but it's over in T, which is where one goes through TSA when entering on the domestic side. Maybe 15 minutes from F by the airport train. It's also "OK"... it's a standard issue American lounge that also can get overcrowded. I haven't been in there since ~2019, but the food was also nothing to write home about. The F lounge food may be a little better.
Generally, though, terminal F is very nice. It's the newest and is spacious. Plenty of places to sit or roam.
I don't care for the BA boarding process... feels kind of chaotic. I attribute that a little bit to cultural differences of people flying BA vs DL, but also the boarding area isn't super conducive to board the way BA (and other airlines like QR) like to line people up. It's hard to explain unless you've experienced it.
TSA over in F isn't bad. In the evenings, perhaps 15-20 minutes max? You can go to:
https://www.atl.com/times/ to see the current wait time...