Eh, sure, I'll toss in my two cents.
I vote Zeus, because...
For ambience...
Working off of the logic present in the
Standard Battle Assumptions, if one side has Regenerationn that renders attempts from their foe to kill them futile, like Wolverine, then KOing them for at least an hour or rendering them unable to fight for a month will do.
Both characters are immortal. Zeus can't die and have his spirit go to Hades, and Cthulhu is sticking around until Azzy wakes up from his fever dream and takes some penicilin. Both regenerate from damage when dealt and can't be put down permanently without the aid of a higher-dimensional being.
So we're running on the knockout laws.
Now then, looking at the AP tables for each, we see that Zeus is Large Star Level (I wuv Typhon's chapter ^_^). Cthulhu is implied to be Star-Level himself, possibly a rank higher.
Eh, close enough.
Speed is likely FTL for Zeus and possibly-really-freakin'-high travel speed for Cthulhu.
Oof.
Now, for durability, we see that Zeus is ranked in at the same as his AP, taking a massive beating from the guy. It was one of his very few losses, having his intestines ripped out.
Cthulhu is... weird...
His greatest durability "feat" was his partial collapse and immediate reparation at the front-end of a boat, which is only because he was still groggy and hadn't quite fully materialized. He's like Buu in that his form is piddly weak (according to the unpleasably herculean standards of this wiki, anyways), but he regenerates so fast that it hardly even matters.
So, according to how I understand it, Zeus and Cthulhu are roughly even in AP, Zeus can strike at FTL speeds while Cthulhu is stuck eating 1d6 investigators per round, and Cthulhu might disintigrate after the first blow while Zeus can get knocked around a bit before he starts to lose his bowels.
So, if Zeus can keep hitting Cthulhu every time he regenerates for anywhere between an hour to a month without getting tired, then he wins.
Too bad Zeus doesn't have a Stamina stat. That's rather unfortunate.
So I vote Zeus.