Here is my take from the perspective of using all three majors (AA; DL; UA). I'm using UA more now and definitely less than AA and staying the course with DL. I pay discount buy up F when I can, use certificates/UG etc when I can and if that does not work grab good Y seat.

AA has slipped. DL stable. UA rising. On FT UA posters tough. UA works best for me to Asia. Beats AA/DL. Can even UG to F often. But 787's to KIX and MEL works. Like the 787 in J. DL tough on UG's from Y, no F UG's of course and J costs more. J seats on UA OK and less coffin like on DL. DL good though and that's why I own DL stock.

UA however better than the past. PDB better than AA but not as good as DL.

But overall UA better. DL solid. AA third.

Just some thoughts. ll