Sonic is OK for fast-food burgers & fries . . . their shakes, on the other hand, have an unpleasant chemical flavor.
I used to say Wendy's was the best of the fast-food burger places, but found out that 1) at the local Wendy's, unless you're there during the rush, you WILL receive a pre-cooked burger that's been kept in the warming oven for quite a while, and fries that have been drying out under the heat lamps for a like period of time; 2) when you order a burger without mustard, you'll almost certainly get one WITH mustard; and 3) there's an 80% chance that whoever's running the register will not speak intelligible English.