Buffalo (really bison) burgers are my top pick. I really like the bite and chewiness of a very lean burger.
Cooked over hardwood charcoal with a generous sprinkling of salt.
Top it with American cheese, iceberg lettuce, tomato, raw onion, and ketchup on a soft white bun.
Lamb burgers would be my second favourite. On, or rather in a pita with chopped romaine, raw onion, diced tomato and green bell peppers, feta, and tsatsiki sauce.
If Im going to have a regular, 85/15 or 80/20 beef burger, I like it on a brioche bun, topped with a griddled slice of either Canadian bacon or Taylor ham, pickled hot cherry peppers, tomato and onion, ketchup and mayo. I sometimes sub bbq sauce or A1 sauce for the ketchup and mayo.
Finally, if I'm forced to eat a turkey or chicken burger, I'd doctor it up with sauteed mushroom and onions, Swiss cheese, and brown gravy on a whole wheat bun.
Oh, I forgot the occasional "4 B" burger cooked over a campfire: Beef, blackened, with bacon and blue cheese on a soft white bun.