I've only had excellent service from agents at the ACs or FLs. One of my home airports being AUS definitely stacks the deck there, because those folks are incredible.
I'd agree with the comments above, 20% of segments have exceptional FAs, 70% of the time they're fine, then the other 10% they're absent/rude/having a bad day. When we fly TATL we almost always sit in the middle seats of the 1-2-1 config, and it's pretty amazing how different service can be in one aisle versus the other. That inconsistency is really the hallmark of AA onboard service, you never know when you're going to draw one of the 10% from the bottom. I don't fly Delta enough to have an opinion, but the spread seems about the same on United.