Easily
In-n-Out since there are none here in Oregon. I can't say much other than the simple delicious combination of meat and cheese is seriously fucking great, especially when that meat and cheese (as well as everything else they use) is all fresh, or at least something that makes it taste really good. That and having the option of stacking 50 patties and 50 slices of cheese in one burger is always nice, not that anyone would do it, having the option is good enough for me.
Plus they're special sauce, some kind of delicious.
And it's funny you mention Sonic, I see commercialls all the time here in Oregon and in Cali, but I have yet to ever see one ANYWHERE in the entire world that I've been, granted I've probobly havent been around as much as others here, I've seen alot and haven't seen one of these.
Jam it back in, in the dark.