I was a long time UA flyer, Global Services member for years. I switched to Delta 3 or so years ago for a number of reasons, erosion of FF benefits, customer service, wifi, culture, all which were justified....and still are today.

In the past year something changed at Delta. I frequently fly from LAX to Europe and return. Delta has become the most expensive options by thousands of dollars on every flight. Seems it's impossible to book a business fare, even two weeks out for less than 9K. I book through a travel agent and they are really good at calling the airlines and getting unpublished fares, but Delta has recently pulled back on those and is holding on to Z inventory as well. Meanwhile between United and Lufthansa I can usually get a RT ticket in the neighborhood of 5K. I do find Delta competitive to much of Asia and Australia.

On a separate and petty note. I influence travel in my organization. When I switched from United to Delta I figured I would be the guinea pig. After my experience I moved 3 members of my staff to Delta. None of us flies less than 250k mqm per year, and one will hit 400k mqm in December. We had these same travel patterns at United, and United did a great job of expressing their appreciation to me. With Delta, I haven't heard a word. Maybe United does a better job of data collection and but I never called them or had to expkain to them that I influenced travel, they just knew. I suspect they noticed i was the first member of my company that flew United, and then the rest followed. Anyway it was a nice touch.