That is a question that cannot be answered unless you define it more!
U.S. Army Rangers....While at Ft. Stewart, Ga. I witnessed "Rangers" live on next to nothing out in the field for DAYS. They all looked like hell if you could catch a glimpse of one of them (almost scrawny looking) but they were incredibly strong.
We had a post "fun run" (yeah right) which was a mini-marathon (13 miles I think)run in BDU's with weapon and pack. I dont remember the times, but my units
competitors (including myself)did nothing but train for this one competition for at least 6 months, and the Rangers STILL literally ran away from us.
MARINES.....I have seen some HUGE Marines. Most have superior upper body strength. Across the board, I believe they have the toughest standards.
AIR FORCE.....The latest "Military issue" of "Muscle and Fitness" had a TON of World Class Bodybuilders representing the Air Force. Much more than the other services. My theory is that they are the only ones that have time to be in the gym every day.
Sorry, guess I didn't help.