I travel a decent amount for business. Meaning I fly 2-4 times a month. Since I live 35 miles south of the Atlanta airport, I use Delta exclusively.
I didn't used to when traveling on personal time. It was all about the lowest fare and getting there during convenient times for me. I used to wonder why people that flew frequently on business loved Delta sooooo much. Now I know why.
It's because they are better, they have the largest fleet, they have the most flights. No, they aren't always convenient, but flying from Atlanta, I can get most anywhere non-stop.
I think they try their best to be the best.
Also - everyone in the air travel industry can spot a veteran business traveler from someone that isn't. It's easy. Also, on a Delta flight, there is a marked difference in level of service with regards to freebies you can get if you are sitting in front of the wings versus not. Sometimes I get on an earlier flight, which I forfeit my "good" seating, so this is a good way to see the differences. Granted, free alcohol and such is standard with Comfort Plus and of course First Class, but there's other small things.