Factually, my money's on the SAS/SBS. They never stop training, exercising, planning and preparing; and they train many other countries' special forces. It's just damn-right impressive.
You hear about their less-successful operations (see: Bravo-two-zero, Arab Spring insertion) but just think about all the successful missions you haven't heard about. The SBS are constantly in Afghanistan.
My leftover trust would be on the: Gurkas (British Army regiment of awesomeness), Spetsnaz and the USMC, in that order.
Edit: Now, that's based on how effective a unit is. If we're going straight for most deadly - I would say the Gurkas.
I mean, just look at this - they're getting rained on by artillery at the start, and they just don't give a shit.
You hear about their less-successful operations (see: Bravo-two-zero, Arab Spring insertion) but just think about all the successful missions you haven't heard about. The SBS are constantly in Afghanistan.
My leftover trust would be on the: Gurkas (British Army regiment of awesomeness), Spetsnaz and the USMC, in that order.
Edit: Now, that's based on how effective a unit is. If we're going straight for most deadly - I would say the Gurkas.
I mean, just look at this - they're getting rained on by artillery at the start, and they just don't give a shit.