Look, special forces have their specialities. Comparing them against each other in a general fashion is pointless. For the USA, if we want to take an airport, well, the Rangers train for that (they sent the SEALs in to do that in Panana and the SEALs, for a special forces team that outnumbered their oponents, got their asses handed to them). You want to take out an oil rig, send in the SEALs. You want quiet recon, send in Force Recon. Hostage rescue, send in Delta. Training the indigenous population to fight for themselves, send in the Green Berets. It all depends on what the mission is.
I do agree that the Spetnaz are likely the most ruthless. Then again, they are a product of the russian military, which has never had a problem with unsafe conditions, ie an American unit has a man die while on exercises, his CO is likely to be in trouble, whereas if it happened in the Russian armed services, his CO would shrug and continue on.