Who was the most powerful god from The Big Three?

Out of Zeus, Posidon, and Hades, I believe that Hades is the most powerful. Not only can he command all of the dead, but he has access to Tartarus. He could unleash all of the titans under oath that they would overthrow Olympus, slay Zeus and Posidon, and let him live. The titans could accomplish this feat with ease should they be released, and Hades is the one who can do that. Even if Zeus and Posidon both layed siege to Hades and his realm, Hades could hold them off with the dead for enough time to release the titans.