A bacon sarnie can _only_ contain bread, bacon, and condiments.
Anything other than bread is an immediate disqualification and it becomes a roll, bap, etc. Toast gets in under a technicality, but is not in the spirit of things.
Adding X as a secondary ingredient would make it a "bacon and X sarnie". Not the same.
Condiments can be any sauces, and include butter or margarine, but they must not overwhelm the bacon in any way.
Under these perfectly normal restrictions, my favourite is white bread with butter and ketchup.
I was thinking this vote would be more about white vs granary vs brown, or brown vs ketchup, not just showing a large selection of breakfast rolls - many of which look tasty in their own right but really aren't bacon sarnies.