I really hate "gourmet" burgers made from lean meat and filled with all kinds of chopped onions, bread crumbs, bacon bits, secret sauces, and assorted other glop that make it taste like a meat loaf.
I like a burger made from not-so-lean beef that has more flavor. All I add to the raw meat it is garlic power and Worcestershire sauce--and I'm sparing with that. And I like them fairly thin and cooked medium. I'd rather eat two small burgers than one sloppy, over-topped, super-jumbo, 2-inch thick, half-pound patty that is charred on the outside and bloody in the middle.
I like grilled onions when I'm frying a burger inside on a griddle, but on a charbroiled hamburger I like fresh chopped white onions, not rings of onions, and I really hate purple onions on a burger.
I like garden tomatoes in the summer, but those greenish, tasteless, hothouse tomatoes in the winter, I leave off and just use ketchup.
Always; mustard, mayo, shredded lettuce, tomato slice, dill pickle slice, and chopped onion.
Sometimes: Cheddar cheese melted just right, steak sauce, ketchup.
Never: bacon, white cheese, fried onion rings, salad dressing, avocados, hickory flavoring