https://en.wikipedia.org/wiki/List_of_the_largest_fast_food_restaurant_chains
I may have missed a few places on the list because I wasn't sure what they were, nor if they actually had burgers or not.
There was also a place called MOS Burger that I skipped because it's only in Hawaii as far as the US is concerned, so I imagine most of us have never had it.
I voted
Five Guy's
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