Each God has its place for certain circumstances. But the one I find the most useful is Hera.
Usually the most dominant alliance will be the most active (and experienced) and plays as a team. Playing as a team is probably one of the most important aspects. But also how quickly your alliance can rebuild its OLU nukes (offensive land units) and how quickly you can rebuild sea units (light ships, biremes, and fast transports or slow transports) determines how much pressure you put on your enemies, how quickly you get BP, get more practice coordinating with your alliance mates (timings of waves etc. ) and rebuild your DLU (defensive land units)
Hera can cast "population growth" spell and cuts recruitment time in half. That means you can rebuild you OLU/DLU in half the time.
The faster you can rebuild the more dominant you can be in your alliance get more BP and get more cities more quickly and put more pressure on your enemies : )
Second most useful is Poseidon "Call of the Ocean" halves the time to build birs/LS and fast transport and is essential to rebuild your navy for the exact same reasons stated above. "Call of the Ocean" is crucial to rebuild LS quickly which allows to conquer cities faster and gain BP more quickly.
It depends what you are after, really. Personally it's down to Hera and Poseidon. Yes, some other gods have better myths, but when picking the 'best' god or goddess, I'd look at utility. Population Growth and Call of the Ocean are extremely important in rebuilding, and Earthquake and Sea Storm are pretty powerful as well. Kingly Gift is also the best value out of the resource spells. So if it comes down to spells, it would have to be Poseidon for me. If you bring in myths, it is a bit harder, as Hera has more accessible and easier-to-use myths than Poseidon does. But I do believe that Hera and Poseidon outclass the other deities when it comes to utility. Hades and Zeus are, in my opinion, the worst as utility tools as, although they have at least one great myth unit each, their spells are a lot more limited in usage and usefulness.
I agree that Poseidon is at the top (definitely in terms of spells). How come you put Athena as worst? Everyone has their own opinion, so I am just curious about what would put Athena at the bottom for you.
I particularly like Hera in the beginning since she provides resources. Artemis, Poseidon, and Hades are also useful when it comes to developing cities/armies. Athena and Zeus are useful for providing quick troops if you need them.