Considering he is a god, I'd expect something a little over the top for him, like Algol, after all, he would very likely be a boss if he entered. I had two ideas:
1 - Spear and Magic - Ares is commonly depicted using Spear and Shield, but I think that would be a little generic for him in SC, since he must feel godlike in comparison to the mortal characters. As such, he could use the spear for normal attacks, and having some magic among his special moves, maybe summoning arrows from offscreen, using fire and summoning chains for his grabs.
2 - Remake of Necrid's kit - Being the god of war, it would make sense if he had all weapons at the same time. Summoning weapons from thin air makes sense for a god, but the moveset would be different than Necrid's, since the latter's was based on SCII weapons. Ares could also have his own different special moves with a little bit of magic here too, so it doesn't end being just copying stuff.