Best burger I've had in NJ is from Stage Left. Have had better burgers than Stage Left in NYC once or twice. But never had better than Stage Left in NJ or anywhere else (but NYC).
It's expensive, but it's almost invariably both huge and immensely flavorful. Out of several dozen visits in recent years, I can only remember a couple times when the burger wasn't absolutely perfect. Although I have to say that, in a disturbing trend, the couple times was among the last handful of times I visited. Hopefully it was a momentary thing and not a long-term trend.
I also like White Rose, but it's more of an experience than a burger. And it's often the gift that keeps giving for days.
Zinburger's Prime-Rib blended burgers are actually pretty good and they do a pretty reliable job of cooking it to order. It's formulaic, and the buns are nothing to write home about. But it's still tasty. Unfortunately COVID has shuttered most of them, at least on the East Coast.
Back in April or May, I ordered a ton of meat from a nearby butcher. The order included, among other things, 10 LBS of ground sirloin and a couple whole filet mignon tenderloins, trimmed and tied. When I arrived to pick up the order, they were still prepping it. And the butcher asked me if I wanted him to grind up the soft fat trimmings left-over from the filets and blend it into the ground sirloin. I did, and he did. That combo made for the best burgers I've ever made (and I've made huge numbers of burgers over the years, trying out all kinds of combos of short-rib meat, brisket, etc. along with various cooking methods and seasonings and prep).