In order:
. I like the color of their planes
. I am one of only 5 flyers who prefer original herringbone to reverse
. I live in Atlanta
On a more serious note, I am fairly happy with DL, but the prices can be over the top. If I move, i would certainly re-evaluate.
I do not understand why people should look for a reason to stay. Despite the "loyality" name on the programs, there is no such reality. Always look around to see whatever works best for you.