Out of BNA, flying UA means "I place no value on the space/comfort that some find when on a mainline jet". The few mainline flights are operated by US to CLT (the "direct" flights on the schedule stop there).

In the interest of full disclosure, I'm one of the BNA-based DL flyers but still carry the AA credit card; I have an itinerary booked on AA for later this month. Even as a low-level elite, I have a phenomenal upgrade rate on DL and tons of scheduling flexibility (the rate is maintained in my signature at the time of posting). I would share my thoughts via PM for anyone interested.