Not sure what the leanest is, but GODDAMN I love porterhouse steaks....damn....as soon as I get off of work maybe I'll do the same. What'd you marinate it with?
Flank steak, hands down. If you cook it right, cut it right, and needle it, it's the most flavorfull cut of meat you can eat. (With the exception of your your favorite lady). Filet has more fat per oz. w/ not much flavor.