I've been thinking of this thread during my trip to NYC. My verdict:
Shake Shack: Awesome burger with cheese, but the bun is just so sweet that it's unpleasant to my European taste buds. Expectation fail
De Santos: NYC Brunch place with "unlimited" champagne cocktails (until you finish their champagne - oops) does a really phenomenal burger. The best I've had in the last year. High quality, done medium rare, full of flavour.