Drumroll, please.
I am one of those extraordinarily weird people whose favorite topping on a burger is... TA DA!!!!
Cheese.
As in, American or cheddar, possibly with bacon. And I agree with you
@JStates -- mushroom and swiss or Muenster are excellent. If I don't think I'll be around too many people for a while, I may even add slivers of raw onion. All perfectly stacked on a lovely brioche or ciabatta bun. Perfecto!!!
But one thing I DON'T want ruining or touching my burgers is any kind of ooey, gooey, slathery kind of SAUCE.
I DETEST a sloppy burger or sandwich. I HATE picking up a delightfully handheld meal, only to have gobs of goo or juice running down the side of my hands. BLECH!!! I don't like mayo, mustard, ketchup, "special" or secret sauce (even if it's a unique in-house creation that the restaurant is known for,) BBQ sauce, pickles, tomato, or anything that will cause my beloved stack of meat and cheese perfection to limp its way into a heap of spongy, soggy nastiness on my plate.
I have had many a waiter raise their eyebrow at me when I order, saying, "You mean, you want it DRY???" Why yes, yes I do, because I want to be able to taste the actual burger -- anything else for me messes up the flavor and texture. Now on the flipside, I've also had to down many a bad burger that would probably have been well-hidden and even pass as edible if only it were smeared with a giant concoction of other pudding-like sauces.
Now, I'm not so picky as to having to order everything specifically to my liking every time -- if we're in a hurry or it's impractical, I'll just order it as is and make do, but I'll scrape off as much gunk as possible and I won't enjoy it nearly as much.
And if my pickiness seems to be a bit off-setting, my family jokes -- and it isn't really a joke -- that I can walk into any place, no matter how supposedly fancy, and all I'll want is a burger (and fries, tater tots, or some GOOD chips -- not too greasy, not too thick, not too thin, and please, NOT BURNT!!!)
But... the sides that SHOULD and SHOULD NOT go WITH a burger? (Including beverages.)
That's a topic for another thread.