Interesting. I have always used ground sirloin (trimmed extra lean) for the meat. Not much for packaged hamburger myself. While expensive, it does impart a really rich flavor.
I like to mix in some salt and pepper, but that is it. Let the meat speak for itself.
Variations include chili powder, onion, and a touch of paprika,
or a little Italian dressing, salt, pepper, topped with Provolone cheese
or a little A-1 sauce, onion, pepper (plenty of salt in A-1), topped with extra sharp cheddar (not melted, but softened).
Condiments are optional and depends on the person. And use whatever bread that does not mask the flavor of the meat.