As discussed, 20% fat helps. But there is more to it. A bigger burger that is cooked well done is going to be dry. In truth, your best eating rare ground meat when you do the grindng yourself!
My answer is smaller burgers with good fat content cooked through. They cook quick enough that they retain their "juicy" flavor.
I sear one side for about 1 minute, and I flip it. If the burger to thick I smash it down at this point, BUT NEVER AGAIN during the cooking. At this point I treat like a pan cake, which is to say I let it stay on that one side until the entire burger is almost done. Then, and only then, flip it back on to the first side to finish. At this point I add cheese (if needed).
That’s it.. 1 smash, 3 flips and onto the BUN. I cook at 425 to 450.