If we go by mythology, Zeus would win hands down. in the Illiad he mentions infront of all the gods that he is the strongest amongst all of them, and even Poseidon submits to his orders to leave the field of war when he threatens him. read more
In Zeus-centric myths, Zeus would win as the myths make him out to be THE God. And everyone kowtows to him. In Poseidon-centric myths, we see Poseidon being stronger than Zeus and the above answer is just Zeus being egotistical. read more
Poseidon would win when the three brothers drew straws to see who would rule it was Poseidon who won however he decided he did not want to rule so he gave the mantle to Zeus. read more
Poseidon, because he is aloud in Zeus's tarritory because it is Olympus, and Zeus isn't aloud in Poseidons tarritory because its the sea. read more