They treated me well for the years that I was a DFW captive, barely scraping out Gold status. They now treat me extremely well as a multiyear CK.
I did a roundtrip on Delta in F with my wife a couple of years ago (had a voucher to spend from when AA rebooked me on a Delta flight, and the Delta flight had issues). Our experience in Delta F MCO-LAX was the worst I had ever had on a domestic flight, mainly because of the terrible family seated in the row ahead of us, and the FA's complete lack of care or control of her cabin. That said, I wouldn't judge all of Delta off of that one flight.
I go out of my way to fly AA... I'd rather do 1-stop in F than non-stop in Y most of the time. Miles are still worth something, and I've paid for so many vacations for my family... no reason to orphan points off to another airline.