Ona semi-serious note, the SAS is probably the best of the groups mentioned, due to a long track record (since 1941) of making life miserable for bad guys from Nazi Germany to al-Qaeda.
The British Special Air Service is one of the most well-known special operations groups. It got its start in World War II, when it carried out numerous missions in North Africa under David Stirling ? making life miserable for the Afrika Korps. The 22nd SAS is the active duty regiment, and has four ?Sabre? squadrons (A, B, D, and G Squadrons), each with 6 officers and 78 men. Two reserve SAS regiments also exist, the 21st (with A, C, and E Squadrons) and the 23rd (with A, B, and C squadrons). When support troops like the 264th Squadron (a communications unit) various headquarters units, and the retirees of R Squadron are added, that the SAS consists of about 1,000 men.
Not as well-known as the SAS, but even more selective, is the Special Boat Section (SBS). This unit consists of three squadrons (C, M, and S Squadrons) and is part of the Royal Marines. SBS members first must undergo SAS selection, then receive additional training in diving, photography, canoeing, and other skills. Among its operations include missions to convince Iraqi troops that amphibious landings were imminent in the 1991 liberation of Kuwait (a mission also performed by SEALs), the liberation of South Georgia during the Falklands War, and covert operations in Northern Ireland.