Delta will constantly improve as profits continue to rise. It only keeps getting better and better over time. New fleets, terminals, more perks and amenities and better customer service.

The oddball out is United which is really the carrier with the most issues and worst service for large legacy carriers now. However it becomes a forced monopoly for some airports and has some additional capacity on certain routes and has some loyal customers and a quality safety rating. Who knows what the future holds but United does have a quality fleet and a large route network.

If I flew myself all the safe carriers are fine to travel with. Depends where you go in and out of.