Good question although I would disagree with the solution if only for the incorrect terminology used.
Buffer Count (Should be BUFFERCOUNT) is going to exponentially increase the amount of cpu used. This answer is correct; although I truly didn't want to select it because of the way it was written, I assumed the question was just as much about syntax as it was about performance.
MAXTRANSFERSIZE, this one is a no-brainer. The way it is written in the question though (Correctly) really makes you question the misspelled BUFFERCOUNT.
BLOCKSIZE is something that is entirely dependent on the media you are writing too, it is very rare to manually change this option. It is best practice to allow the engine to determine this on it's own. Am I incorrect on this?
I can't understand why compression was left off of the list. There is no single option that will decrease the backup execution time as much as this will.
I love these questions, but I wish they were reviewed a little closer for the grey wording that exists in so many of them!