Who are the toughest US Special Operations Force?

SEALs, Army Special Forces, Marine Reconnaissance, Pararescue Jumpers and Combat Controllers (PJ/CCT) all are the same but in different uniforms. Seems that youre looking for a black white answer but its really not important. All have same training. Air Force does get the highest academic types from college and high school. They make very good agents after leaving the service - CIA, FBI, narcs.

Sea duty is hard and Army, Air Force, Marine personnel don't do it, though they scuba as much as Navy people.
Israeli commandos regularly train with PJs/CCTs and they make the toughest commandos