For most of the people on this thread, there's been a fundamental misunderstanding about what special forces are. The SAS in Britian is a special forces anti-terrorism unit. In the U.S., Army Delta Force, Navy S.E.A.Ls, Marine Force Recon, and Air Force Combat Control are NOT special forces. The only special forces in the U.S. military are the Army Green Berets.
Also, the only anti-terrorism units in the military are Delta Force and S.E.A.L. and S.E.A.L. is not generally trained in anti-terrorist operations, but rather in infiltraion. Delta Force is the only unit comparable to SAS, and they usually work WITH the SAS. Also, most of their missions remain classified, and the Pentagond officially DENIES THEIR EXISTENCE.
Combat Control is trained for painting targets and air assault to take over airfields for use by the Air Forces other assets.
Force Recon is used to disrupt enemy emplacements, command and logistics infrustructure, in preperation for a forced landing.
The REAL special forces, the Green Berets, are trained to go behind enemy lines, train insurgents, and disrupt the enemy. During Vietnam, they had a kill ratio upwards of 1000/1, not that kill ratios win wars. In Afghanistan, they were instrumental in preparing the Northern Alliance in it's operations against the Taliban. You must speak two languages fluently just to be considered for entry into the Green Berets and you cannot apply. You are chosen. They are made up of the best of all other services, save the spec ops (which, by the way, is the designation for the Delta Force, S.E.A.L.s, Combat Control, and Force Recon). What follows is over a year of some of the most intenst training in the world.
Basically, it's foolish to compare Special Forces, because our Special Forces are trained for different reasons then other nations special forces. Delta is not as good as SAS, but it would be very hard to guage their effectiveness since they are the most confidential unit in the U.S. But ultimately, comparisons are futile