Who has the better left hook?

I agree with this. As far as technicality and damage is concerned, this has to go to Cotto - his left hook is brutal and he also rips it to the body as well as the head. Floyd has a very quick counter shot, but he generally doesn't dictate a fight with his left hook, he uses his right hand more and his jab to the body with his right upper cuts to do the owning. Cotto's left hook is dominant though.