No disrespect intended but not in a million years.
The training and equipment of American Delta units blows away British SAS & SBS. The Russian have good marksmen but their equipment is nowhere near comparable.
I would place them in groupings...
Delta, Green Berets
Seals, Spetnaz, SAS & SBS, Marine FAST Companies
Rangers, Marine Recon
The American and British units all have ongoing combat experience through Afghanistan and the Phillipines. The Russians are playing in Chechnya...but they dont use SpecFor like the west does.