Actually, the real most badass ones are the ones we have never heard about.
That would be
ME. You do not want to mess with me, buddy. For starter, I know marital arts...er...I mean martial arts...that not even Asians can pronounce.
But seriously, the phrase 'special forces' have been tossed around carelessly.
In the US military, there is only one 'Special Forces' group, and that is the US Army's Special Forces, aka the 'Green Berets'. By the way, SF-ers do not like that label. They will patiently tolerate civilians using 'Green Berets', but they will correct any military member who calls them that.
Other famous groups like SEAL or Rangers are correctly called 'Special Operations' groups. SO groups take existing skill sets and expand them to absurd proportions. The Rangers could be called 'extreme infantry'. The USAF's Combat Controllers are 'extreme air traffic controllers', Pararescue are 'extreme medics' except that they are not true medics under the Geneva Conventions but line combatants with extreme combat medical training.
What make the US Army's SF group truly a 'special forces' label is that their skill sets contains skills that are outside the standard US Army skill sets. For example, you do not need to be multi-lingual to be a Ranger, but you have to be multi-lingual to be an SF-er. You do not have to be familiar with local and global politics to be a SEAL, but must to be an SF-er.
All these images seems to denote extremes of basic combat skill sets, which make the unit more like 'special operations' groups, than 'special forces'.