My favorites:
Home-grilled or nicer restaurant burger - brioche or potato bun, preferably toasted in butter, medium/medium rare patty, tomato, dill pickle slices, lettuce, mayo and ketchup on the top bun. More ketchup for dipping. I leave the bottom bun naked so it doesn’t fall apart. Cheese is usually too much for me with a rich, thick, juicy burger. I’ll make exceptions sometimes for a burger dressed with barbecue sauce and cheddar cheese or a patty melt with grilled onions, mushrooms, and cheese. I like a fancy remake of the Big Mac if done well.
Fast food/diner/smash burger - these are drier, so I spring for American cheese. If available I’ll add lettuce, tomato, mayo and bacon (Wendy’s Jr. Bacon Cheeseburger is a happy childhood sense memory).
I never put raw onion or mustard on a burger voluntarily. And I detest the minced, dried onions that McDonald’s puts on their burgers.
