Delta did some unexpectedly nice things for us a while back, my wife is committed to them. I also think they do a solid job overall with a few exceptions. Their people seem to "care" about as much as can be expected.
When we flew to Istanbul through Paris, my wife for some reason took her French passport, not the US. Flying out was not a problem, flying back was. Turkish Air would not let her board to Paris to ATL with her French passport, it was a mess. We bought a separate ticket to get her to Paris where at least she speaks the lingua Franca. We get to Paris and I figure I'll see her in a couple days, I go to the lounge and then am standing in line to board the flight when she shows up and says she was cleared to the US and they had kept her seat next to me. She said a Delta agent in Paris went out of her way to help her get the credentials. The crazy thing is she has Global Entry, so we got to ATL and that card is all she used to get through anyway. But this isn't the nice thing they did in the past.
Now I always ask if she has the US passport. I'm looking forward to Vienna in a couple months, I snared seats in Premium for $1500 after a $500 credit we had.