Would have to say Steak 'n Shake from this list here, mostly because I can't get it in my state. Love their chili and their bacon steakburgers.
As far as what's available in my area, I would have to go with:
-In-N-Out
-Rally's
-Carl's Jr. (What they call Hardee's west of the Mississippi)
-Sonic
As far as what's available in my area, I would have to go with:
-In-N-Out
-Rally's
-Carl's Jr. (What they call Hardee's west of the Mississippi)
-Sonic