You are mixing stuff here, I think. SAS, Delta and Seals are special operations teams. They go in in small numbers in commando-type raids. Gurkas and Green Berets are closer to classic soldiering, although maybe somewhere between the two. I sure would not want to piss off a green beret!
Among Special Ops, I'd say the SAS. They have more experience at special Ops than anyone else, and have been doing it longer (established in WWII, I think.).
The only thing you should feel when shooting a terrorist: Recoil.