just got back from a burger run and had one @ BK, a VERY tasty fast food sandwich, it's 100% better and certainly best if you ask them to cook it up fresh for you as opposed to taking a cooked fillet out of one of those heated drawer systems they use now.
EDIT:
Fair warning in case you're in a hell fired hurry, having one cooked fresh is a solid 5 minute wait but well worth it.