ok i seen this kind of thread in other forums dozen times. There is no best, only SOF that suit one's operational requirements. You simply cannot compare SEAL teams with Green Berets, because their primary mission is different. And even though SOF from different nation has a similar mission role, their training, doctrine, and equipment is different from each other and therefore cannot be judged unless one is proven to be the most effective in combat. I'll list some of the SOF around the world for you and specify their primary mission.
CT=Counter Terror, SR=Strategic Recon, DA=Direct Action
UW=Unconvential Warfare, CA=Civil Affairs, PSYOPS-Psychological Ops
Alfa Team-CT, DA (Russia)
Spetznaz-DA,SR,UW (Russia)
Delta-CT,DA (U.S)
SF Airborne-UW,CA (U.S)
SEAL-DA,SR (U.S)
SAS-CT, DA,SR (Britain)
SBS-DA,SR,UW (Britain)
SASR-CT, DA,SR (Australia)
JTF-2-CT, DA,SR (Canada)
Unit 777-CT,DA (Egypt)
GIGN-CT (France)
13 RDP-DA,SR (France)
GSG-9-CT (Germany)
KSK,-DA,SR (Germany)
GROM-CT,DA (Poland)
Sayeret Matkal-CT, DA, SR (Israel)
Paras-DA, SR (India)
There are plenty more, but these are the more well known ones. Hope my reply helps you to understand that this kind of comparison won't go anywhere except causing arguements in the forum.