My vote goes to XSG Dumpling House on 53rd St. You only get 4 for $1, but they're pretty big, the filling is very moist and flavorful, and the skin is really delicate but still with a little satisfying chew. Most times I've visited, the bottoms have been fried a perfect crisp golden-brown.
I had the opportunity recently to compare them with Prosperity's Sunset Park branch, which I'd rank as the close second in the neighborhood. When I did the A/B, Prosperity's wrapper was not quite as tender and felt a little bit gummier.
I'd put Kai Feng Fu next after Prosperity, and then Family last.