I use a combo of WN and UA. If you can do a Business Select fare on WN, that's pretty reasonable as you likely will get an aisle/window in the first 6 rows. I have the UA Explorer card as well. Too bad the AA partnership is basically going away, but if you can get an AA codeshare that might be a decent option.
Did fly Delta a little while back when I had to get to DLH. Even as a regular member it was ohhkaay for one trip.
Answers change if you are flying internationally, but assume you mean domestic since AS has multiple partners internationally.