I'm generally OK with whatever. I'll take a "normal" burger (cooked to medium). Most condiments other than mustard are good. No pickles, no un-cooked onions (caramel onions very good tho), but all other toppings you could put on there. lettuce, tomato, avocado, cheese, jalapeño, egg.

I'll occasionally get a bean burger / meat substitute burger, which I also think are pretty good.