Hey, since Might is now on the subject, what about Cyclone's questions of using Might in combat? Like combining tons of Might into a fireball or something. How much impact will that have on combat?
Levels - mean that a god is inherently stronger, has more Might anyway and is just in every way more powerful than the other and therefore should, if they use their strength correctly, come out on top. At worst, they can force the other to spend all their Might and then take them out with their own remaining Might.
Might - The more of it you have, the more powerful the strikes you can deliver. An attack which uses 5 Might as Cyclone suggested could obliterate entire Solar systems. If an attack using higher Might, or an army with higher Might, goes against one of less Might, it will generally win out, unless there is space for tactics and strategy to play a role.
Tactics and Strategy - This is really about the individual and how smart they can be about their battle. If they are very intelligent about it and deliver one act of genius after another, whether they are high or lower level, things should swing in their favour whether due to their brilliance alone, or due to some kind of divine intervention in their favour.
Writing quality - This is just a matter of pure writing quality. Is it gripping? Does it make sense? Is it well thought out? This will be a factor a GM considers when deciding who should win.
Plot line/Player agreement - If the players have agreed what the result will be, then that is that (unless the result is really weird. Like a frail old mortal lizard which can't think and has no magical powers going up against a hero and winning.)