Kaiten geri to the temple + it looks awesome
I vote for a strong back-kick.
For me, those have been the hardest hitting kicks.
Capoeira has some of the strongest kicks due to the amount of momentum thrown behind them - they look cool but they are totally impractical and have very low percentage chances of successfully landing in a real fight. Not exactly scientific journal worthy but here is a Capoeira low kick on Fight Science vs some other styles:
You won't find many Capoeira knockout kicks online which shows just how low percentage they actually are but here is a good one:
For me I think the strongest kick I can throw is a 360 kick, but **** if I can aim it. Other than that I would say a good jumpside/stoppage kick tends to have good follow through for power. Unfortunately most strong kicks are also heavily telegraphed.
My strongest kick (Force wise) is definitely a back kick/turning sidekick.
Also, I think it's worth noting that on the Fight Science video the TKD guy's roundhouse hit harder than the Capoeria guy's, and TKD is not typically known for it's power.
Angle kick (with shin) or step through sidekick. An axe kick to the face can do some major damage as well.
Yap Chugi - Side Destroying Kick