Wich crankset is the stiffest?

Chechel

After some research, i have a problem with choose "hardest" of all the road crankset. its all known that find weight\ cost\ bcd of each is not a problem, but what about the stiffness?

I find most good variation of powermeters( assioma don't get in this list) for laboratory and something about good wight, accuracity, but i don't have any idea where is information about differents between Dura-ace and FSA K-Force team in terms of stiffnes.