Having researched myriad of documentation regarding special forces and debates played out in various forums I have come to the conclusion that it's a pointless exercise trying to establish which are the best of the World's special forces seeing as most of their missions are secret and we will never get to hear about their successes or failures.
The only comparisons that can accurately be made are in cross-training exercises and as has been mentioned, the British SBS, (Special Boat Service), trump the Navy seals in a high percentage of exercises.
In a war scenario It would be as well to throw the names of these regiments into a hat and pull one out as it will be just as accurate as trying to argue a case for your countries SF to be accepted as 'the best'.
These arguments are mostly borne out of National pride for respective SF and not through any extensive knowledge of their capabilities. Unless someone has served in that environment and has a working knowledge of other SF capabilities then it's akin to shouting, 'my Dad's bigger than your Dad'.