23 Toughest Militaries in the World, 19 Sep 2014 by Caitlin Bussmann
http://www.rantpolitical.com/2014/09...blade#slide_47
I don’t know how scientific this is but at least it ranks the U.S. as #1 because of a “Defense budget five times larger than the closest competition.” China and Russia came in second and third, with Iran (#17) and North Korea (#18).
I assume, with looming budget cuts, the competition will get much closer (according to this scientific study).