RIght now the military is cutting down, so the amount of people they are allowing in is limited. Each of the services offer different experiences. You should first figure out what you want to do in the military, then pick which services suits you. Like me, for instance, I want to fly, so all the services are available to me; however, for my friend who wants to be an infantryman, the Army and the Marine Corps are his strongest choices.
-Army = basic military. Easiest to get into, higher PT standards than the Air Force and Navy, but currently less than the Marine Corps. PT standards are expected to surpass that of the Marine Corps PFT due to the Army getting more selective. The Army offers the broadest range of jobs, everything ranging from accountant to astronaut.
-Navy = travel options. The Navy has the easiest PT standards, but is more technical than the Army, which means you need better high school grades and a better ASVAB score, but that doesn't mean you'll get turned down if you're not Albert Einstein. The biggest benefit of the Navy are the travel options, since the ship-borne Navy deploys every 6-12 months, you can expect to be at sea for about half your career. The Navy hits ports around the world, making a unique travel experience unlike any other. However, this is also the biggest downside, as the cramped confines of a ship are not everybody's cup of tea. If you like water, you like travel, and you're not too thrilled about humping 12 miles with a ruck sack, the Navy is for you.
-Air Force = most technical service. The Air Force is our most technical service, meaning you need to have a high ASVAB score to qualify. The Air Force basic PFT is the 2nd least challenging, right in front of the Navy PFT. Most air force jobs go towards the maintaining of the flying air force. Most airmen will work with or around aircraft. The Air Force also treats is personnel the nicest. Air Force bases always have good chow, running water, and good barracks. The Air Force does offer a wide range of jobs.
-Marine Corps = most military experience. If you want a true military experience, as in, you want to live, breathe, eat, and sleep military, then join the Marine Corps. The Marine Corps currently has the highest PFT standards, and is typically more strict on a daily basis compared to the other services due to the common feeling of camaraderie between Marines. The Marine Corps believes in "Every Marine is a Rifleman," so you can expect to have to do a lot of physical work, even if you're cook. The Marine Corps offers great travel experiences because of its relationship with the Navy. The Marine Corps offers a variety of jobs that compares in scope with the Army, since the Marine Corps operates aircraft, land vehicles, boats, and maintains a ground fighting force. The Marine Corps is a middle ground in intelligence. You don't have to be the smartest guy ever, but you can't be a total meat-head.