All these suggestions, oy!!
What I have seen, as we get older, and with more disposable income is that we have moved on from the 70/30 ground beef and gone to 85/15 or even leaner. That is where the rub is, you lose the fat, but you lose the flavor also.
What I have been doing recently is replacing some of the fat, I will put 1-2 tablespoons, (I think, actually it is a glob), of butter, yes butter, real butter from cows, in with the meat before mixing. Not that stuff being passed off as spreads or margarine these days. It seems to help with the flavor and keeping the meat moist. Other than that, I am pretty basic. Ground black pepper, butter, a pinch of salt and off to the grill.
Wow, who would have known you could write that much on what to put in a burger. Esp when it is only 3 things!!
bob