Consistency wise in modern world, they are the best.
But i wonder what "special forces" is the best?
Idk, because in all lengths special forces really just means outside of the normal military.
But then would spies count? Or Hitmen? In a modern world where bullets can hit from so far away, and people have finally understood the combat involved with them, special forces are really everywhere and even the pros can get shot. Consistenly navy Seals have proven to be the most effective, but the best?
Idk what actually constitutes the best since so much training still doesn't mean actual combat record.
I'd have to say either US Navy SEALs and the 1st SFOD-D or Russian Spetsnaz. Navy SEALs for their grueling training, efficiency, record, their "in and out" capabilities. 1st SFOD-D for the same reasons as the SEALs (although this is a HIGHLY classified divison, NO ONE can know if you are a SFOD-D operator). 1st SFOD-D trainees must show 100% accuracy in shots up to 500 meters, stationary and moving, otherwise they cannot continue. All trainees come 75th Ranger Regiment or the US Army Special Forces.
Finally, Spetsnaz, for obvious reason. Their sheer brutality, efficiency, indifference to pain... and they're Russian. Enough said.
Id tell you but then id have to kill you.
But seriously, coming from me being a Russian myself and my family being in Russian military, all of them getting Purple Hearts and so forth.
Spetsnaz. And not the Spetsnaz you see in COD thats shit, im talkin true Russian blood that breaks necks for fun.