Which branches of the military have the most rigorous to the least rigorous military basic training?

#1, at 2 years 15 months before they receive their Beret signifying their completion of training, The United States Air Force Pararescue Jumpers have the longestng of them all.

#2 As far as Basic Training is concerned, every Basic Training/Boot Camp, is challenging in its own right. All branches, Marines/Air Force/Army/Navy/Coast Guard are all in their own right challenging and will demand only the best of the individual. All branches are strenuous physically and mentally all at the same time. Marine Corps Bootcamp is 12 weeks long. Almost immediately after "Receiving" Week, you begin Combat techniques and Marine Corps Core Values. In fact, three entire weeks you are on grass/rifleman/eval phase. Navy Basic Training is about 9 weeks long. Their ENTIRE basic training is located inside of buildings called "ships". The Air Force has been beefing up basic training over several years. Never once has basic been "easy". USAF Basic training is now 8.5 weeks long. However, during the testing phase of this change officialized in October of 2008 (Started in November of 2005), the original 7 week long basic was put into over time to test out the changes that are now implemented. Changes such as, Pugil Stick fighting, Hand to hand combat, and a three week field training spread. Demand or level of it is a matter of the individual service member. Length of training is easier to measure:

Marine Corps : 12 weeks

Navy : 9 weeks

Army: 9 weeks

Coast Guard: 9 weeks

Air Force : 8.5 weeks

The U.S. Marines have the most physically, mentally, and emotionally challenging boot camp at 13 weeks. The Army (10 weeks) is next, followed by the Navy and Air Force ( each 8 weeks). Note that Marine boot camp emphasizes marksmanship, leading the the well-deserved credo 'Every Marine a Rifleman" as they prepare EVERY Marine for possible combat as compared to less than 25% Army, Navy, Air Force .