Which one is it?

Rarely if ever

Edited to remark that after a bit of rumination it's apparent the q was meant facetiously, as a comment on the logic of our language; so thanks again to the a2k participant for making the rest of my dreary day

On the 4 v 6 however I'm not so sure; so let's assume it's in all seriousness

Suspect four might provide a tinge better mileage, depending on relative sizes but it's a toughie since so many factors besides the number of cyls affect mileage;

http://able2know.org/topic/228117-1#post-5509075

…….so let's have some input from the more nearly expert

The Porsche I can't afford seems to do quite well on 4 cyl

Well, here you have four cylinders coffee cups to keep your coffee hot.

(Hot rods not included).