McDonald's. Because everything seems to be made of all of the same stuff.
The Burger King triple Whopper with cheese is truly a thing of beauty. Wendy's does everything pretty well. Frostys are wonderful. Arby's specialty sandwiches are very very good. Subway and Taco Bell are just okay.
Big picture I really don't visit chain fast-food very often. Grocery store delis are often a favorite of tradesmen. And Mom and Pop gyro shops, carry out Mexican, and those little hole-in-the-wall hot dog joints are always the first pick.
Burger King, that and California Pizza Kitchen are the only two places to eat near my work. I dislike CPK, so that means I've eaten at BK so much now I hate eating there.