With Ares at the centre of G Willow Wilson's new Wonder Woman arc, the choice is again made for me:
Ares
Let me start with saying that I probably have a different view of Ares, and his development as a god, than most of you. My background in Norse mythology means that my impression of Tyr might colour some of my assumptions, especially when it comes to viewing how Ares would view the concept of justice—something which is central to Wilson's imagining of the character. However, I also believe that specific view might drive the future conflict between Ares and Wonder Woman: we will see how it goes, or Read And Find Out, as Robert Jordan used to say.
Ares is one of the twelve gods and goddesses of the Olympos, but like Hestia his place there is a bit ambigious. He was not widely worshipped, and even the other gods (with the exception of Aphrodite) apparently hated him. He was the personification of bold force, courage, and strength, and was not so much a war god as a god of destruction. Thus he covered the tumult, confusion, and horror of war, but sometimes also plagues and epidemics. But he was also a god of both civil order as well as uprisings and riots. This again shows the way that Greek gods often were more connected with fields of responsibilities rather than specific outcomes.
Some of the epitaphs used for Ares were beastly, bloody, manslaughtering, and stormer of cities/walls.
Among the myths connected with Ares we find that he is jelaous of Adonis when Aphrodite took him as a lover. Ares transformed himself into a boar or bear and gored Adonis to death. But he also is unique in defending his daughter Alkippe against rape—something which was virtually unheard of for the male Olympian gods. Many myths also describe how his rash or foolhardy actions in war cause him injuries or causes him to become captured.
According to several sources, Ares was worshipped by the Amazons. Penthesileia was said to have been his daughter, and later sources described all of the Amazons as his daughters. Hippolyta is also described as carrying the belt of Ares and of being Ares's daughter by a late source.
Before I go on with possible re-imaginings of Ares for Wonder Woman, here is an aside into comparative mythology, because Ares has clear counterparts in other mythologies: in Roman mythology Mars, and in Norse mythology Tyr. Within Georges Dumézil's classification of Indo-european gods, there are far more possible counterparts to Ares, though that hypothesis is not without flaws or detractors. However, with Wilson picking up justice as Ares's new thing, looking to those other gods might be interesting, because they are much more about social order and justice than Ares is.
In Norse mythology, Tyr is described as both brave and sensible, but also as someone who cannot create peace. But he is also strongly connected with the thing, the early form of democracy found in Norse culture, which acted as a forum for peacefully solving issues and determining fault in crimes. As such, he was connected with the judges. In a way, he was not so much a god of justice as of the right to decide what was right or wrong. Likewise, the Roman Mars was both a god of war but also a god of treaties (and thus peace). He was also the god of victory in war, something which is missing from the Greek Ares.
So how to bring all this into the Amazons and Wonder Woman? Pérez's war god Ares was in many ways rather close to how the Greeks imagined him, but I think missed that an essential part of his nature was destruction. The Cold War that Pérez used as a backdrop is to me much more a corruption of Athena's warlike nature of strategy and cold reason rather than something that comes from Ares. And the fact that the Greeks mistrusted a god that was so closely associated with the Amazons makes me think that there are aspects of Ares that the patriarchal Greeks suppressed.
One way could be to imagine the Amazon Ares as a god who embodied strength, courage, and destruction, but who recognising it also placed himself under the guidance of those more level-headed than himself, something which would be an extremely Marston-y concept. To a patriarchal society, such a god would of course be anathema. If Wilson chooses to go all the way there, my hat will go off for her. On the other hand, I expect that such a re-imaging will be a little too radical. Instead, I imagine Wilson will rather play up that Ares will more be focused on the right to make decisions of law rather than justice in the modern sense.