This is the deli of my youth and thus the one I compare all delis to. It's tough though because when I come home for a visit it's typically during major (usually Jewish holidays) so the entire world is there waiting. Salivating for their matzo ball soup and corned beef sandwich.
If you dare to brave the lines (or are lucky enough to live in the area) then I would highly recommend a few of their traditional menu items - the matzo ball soup, the corned beef and latkes, the blintzes or the matzo brie. Make sure to grab some treats from the bakery (russian tea biscuits or black and white cookies) before you hit the road.