Hands down, choice flank steak. Too bad it's gotten so expensive these days.
Been using it for years. Cut it with the grain, in 1/4" to 1/3" strips. A while back, Alton Brown did one of his shows on finding the best cut for jerky and he concluded the same regarding this cut.
Take out of smoker when the meat still has some moisture in it. It should be to the point where it still has a little give and not bone dry.