I'll let you in on a little-known secret. There aren't any "best." It's like asking which is the best doctor, a brain surgeon or a heart surgeon? Both are doctors. Both graduated college, and then from medical school and then successfully completed a residency. Both have the skills and knowledge of general medicine. Both can diagnose and treat many illnesses, even those outside of their primary specialty. However, each are "best" in their specific specialties.
Special Operations Forces are just like that. Each are highly trained in general combat and small unit tactics. Each one can be used for many general special operations missions. However, each Special Operations Group is primarily trained for specific type missions. If one wished to attach explosives under the water line on an enemy ship, for example, Army Rangers would not be the best choice. In this instance, the Special Operations Force with the most training and experience in underwater combat operations would be Navy SEALS. On the other hand, if one needed to deploy a highly trained light infantry force well inland, behind enemy lines to destroy a significant military target, you can't do much better than a company of Army Rangers.
Let's take a look at United States Military Special Operations Groups:
Army Special Forces
It's quite common for the layman (and the media) to refer to all Special Operations Forces as "Special Forces." However, there is only one real "Special Forces," and that's the United States Army Special Forces, sometimes referred to as the "Green Berets." The other "elite" military groups are more properly referred to as "Special Operations Forces," or "Special Ops." It may interest you to know that many Special Forces soldiers don't like the nickname "Green Beret." As more than one has told me, "A Green Beret is a hat. I'm not a hat. I'm a highly trained, professional Army Special Forces Soldier." The first Special Forces unit in the Army was formed on 11 June 1952, when the 10th Special Forces Group was activated at Fort Bragg, North Carolina.
It may also interest you to know that the primary mission of the Army Special Forces is to teach. Yep. That's right -- they're all a bunch of teachers. So, why are they "special?" Because they do their teaching right in the middle of combat missions. They go right into combat situations with military members of friendly developing nations and teach them technical fighting and military skills, as well as helping them resolve human rights issues during combat operations.
However, like all Special Operations Groups, that's not all they do. That's just what they do best. When not teaching foreign military groups how to sneak up on the enemy and kill them without dying themselves, Army Special Forces have four other missions that they do very well: Unconventional Warfare, Special Reconnaissance, Direct Action and Counter-Terrorism.
Unconventional warfare means they are capable of conducting military and paramilitary actions behind enemy lines. Such actions could include sabotage or helping convince rebel leaders to fight on our side.
Because all Special Forces Soldiers are qualified in a foreign language, they are tops in many aspects of Reconnaissance. They can intermingle with the local population and discover information that would be impossible with other types of "recon."
Until relatively recently, one could not enlist into the Special Forces. One had to be in the rank of E-4 to E-7 (for enlisted members) just to apply. That's still the requirement for those who are already in the service that want to apply for Special Forces. However, in the past year or two, the Army initiated the 18X (Special Forces) Enlistment Program. Under this program, an applicant will be trained as an Infantry (11B) Soldier, then sent to jump school (parachute training). He will then be guaranteed the opportunity to TRY OUT for Special Forces. This means he will have to complete the Special Forces Assessment and Selection (SFAS) program, which has a very high wash-out rate, even for experienced soldiers.
If, by some chance, the wet-behind-the-ears recruit can make it through SFAS, he must graduate the Special Forces Qualification Course, which (depending on the exact Special Forces Job he is training for) is between 24 and 57 weeks long. Finally, he must learn a foreign language at the Defense Language Institute. Depending on language, this training can take up to a year. If he fails any part of this training & selection process, he is immediately reclassified as an 11B Infantry.