As a Manhattan resident, allow me to weigh in…
I love the McHale’s burger. It’s relatively little known, so I’m impressed that Flatted Fifth knows of it.
A relatively new place worth trying is the Burger Joint, located in the Parker Meridien Hotel (118 W. 57th, around 6th Avenue). One of the neat things about it is that, while the hotel is fancy, the restaurant is most definitely not. It’s the size of a postage stamp, and offers the following: burger, cheeseburger, fries, brownies, milkshakes (after 3 p.m.). That’s it, other than soft drinks and various condiments for the burger. It’s really good, inexpensive and worth the visit.
Another fun place to try in NYC is Prime Burger, on East 51st Street between Madison and Fifth. The burger is just OK, in my opinion, although others loves it. The reason to try it is because of the wacky set up. The front of the restaurant offers 50s-drive-in style seating (or, if you prefer, school-room style). You sit in a one-person booth, with a swivel tray.