I use both cards, AA/Citibank and DL/AMEX. I collect the DL/AMEX points during promotions such as double or triple buy anything to gather quick points. I usually purchase I bonds during these promos. I don't fly DL as my preferred airline is AA. I'm collecting the DL points for trips to Europe or to give my mom a BE ticket to FRA every year. When the DL promos are not active I use the AA/Citibank card exclusively and for several reasons. The lifetime gold opportunity, the frequency of flights out of AUS, and the better legroom in coach.