Originally Posted by
Elchupanebre4
I'd argue unless you are going international Southwest is a second viable option. Even as a 1K upgrades on United out of DEN are a bit tough unless flying off business times, but I've done both AA as primary (with SW domestic as second) and UA/SW. as long as you ahve either SW or UA you are well set on Domestic options.
Granted, as long as you can handle SW's eccentricities.