if you factor in some more criteria besides physical fitness/fighting, weapons handling and their weaponry arsenal, there are immediately a couple of big contenders like navy seals or spetsnaz who'd immediately fall out of the boar.....
think in terms of:
Psychology, interpreting the intentions of both friend and foe, negotiation tactics, learning how to withstand "interrogation", learning how to start/stop riots/uprisings, etc...
Languages ? several arab dialects would give special forces a huge advantage in theatres such as iraq or afghanistan....
Medical training ? being able to treat your wounded in an improvised "ER" without the need of immediate evacuation can give you a huge advantage and may be the difference between mission success and failure....
Use of weaponry/machinery (see mcgyver/a-team)
Escape, evasion, infiltration: how well can they "blend" with the natives to acquire information or perform other objectives....
Special tactics?
are these forces trained to use a variety of vehicles?
Underwater warfare/demolition/construction/infiltration
Halo/Haho jumps
and other insertion methods...
etc....
etc....
even tough these criteria might not necessarily attribute to how "deadly" these forces are, but they definately attribute to how effective they are in executing their missions on the battlefield...
In a lot of their missions, be it recon/demolition/rescue/etc , they usually try to use the least ammount of deadly force possible, cause for these folks the mission is the nr1 priority, and you'd be amazed how few missions actually are about "killing", usually the "killing"part is just a means to get their goals...
