So lots of people are posting Lovecraftian gods, but do fictional gods count in this thread at all??
And inb4 the obvious atheist response to this, by "fictional gods" I am meaning gods created specifically as part of a fictional work, intended as fictional by their authors.
If the only the "non-fictional" gods count, I think the battle would go something like this:
Either Shiva or Sutr or the like opens with an attack that annihilates the whole universe, as it is within their power to do so. Whichever world-ender god launches their attack first probably destroys the others.
I think the Nahuatl ("Aztec") gods survive the initial world-ending attack (they also have the ability to survive the destruction-cycles of the universe), but they no longer have a source of mortal sustenance and so they would likely die if left alone too long.
Aegir, Vidar, Vali, Hoenir, Vili, Magni, Modi, Hermóðr, Forseti and Ullr of the Norse pantheon also have the ability to survive an apocalypse, so they are fine as well.
If Shiva gets his attack off first, after the destruction of the universe he becomes Brahman and goes about recreating it, then becomes Vishnu.
If this happens, the Nahuatl Gods have a chance, as they have a supply of blood.
Ultimately I'd say Vidar is the strongest surviving Norse god, Huitzilopochtli the strongest surviving Nahuatl god. I think Huitzilopochtli could easily end Vidar in a one-on-one fight. However I think Vishnu beats both of those fairly easily, so Vishnu wins this scenario.
However, if one of the other universe-enders gets off their attack before Shiva, like Sutr, for example, then I think Vidar wins ultimately. I don't think he could take out Huitzilopochtli in a fair fight, but he just needs to avoid engaging with Huitzilopochtli until the left-handed hummingbird starves without mortal bloodshed to feed off of.
I think Vidar then gets the mantle of Nahuatl Sun God, by the way that that title is usually transferred via apocalypse??
So if Sutr is faster than Shiva, Vidar wins.
If Shiva is faster than Sutr, Vishnu wins.
That was a fun scenario to contemplate.