It depends on the dog, bun and cooking method to me.
If I'm dining at a new hot dog establishment for the first time I want to try them 4 ways.
Plain - to see what you're working with.
With Heinz ketchup - no other brand will do.
With chili, mustard and onions - now we're getting serious.
With chili and cheese - my current favorite.
Then figure out which combo of all of the above works best for the location and repeat.
Toasted roll sometimes, steamed others, New England style lightly buttered with a roller grilled dog works nicely.
How about right off a stick over a bonfire?
Pork & beef first and foremost, all beef next, venison dogs a distant third, turkey dogs if that's all there is, I guess.