Okay, just read a wiki for both.
Pyramid head, is just damn epic. He not only rapes and slays people, BUT OTHER MONSTERS AS WELL! He carries an oxymoron as a weapon, a "Great Knife." Like a "Giant Hamster" or a "Massive Pinkie." And he rapes people with a spear, too.
But Sephiroth is a super-human, almost God. He battles at high speeds, flies about, throws energy around like a angry crack ho. Pyramid Head is almost a psychological weapon. James outruns him, he twitches a lot. He's a selectable character for Track & Field. He's the stuff of nightmares, but outside the dream world, exposed to the sun, I imagine he wouldn't be half as terrifying. Which is not to say he's not brutal, shocking, and utterly horrifying. I'm just saying he's twice as much so in an ancient, dark, rusted theme park, crawling with hordes of demented, gibbering, cackling demonic entities.
Besides, Sephiroth was almost a god on many occasions, I don't imagine he'd be phased by inflatable vagina monsters like I was.
So, reluctantly, despite the Awesome Factor, my guess for success goes to Sephiroth.
I'm still on Pyramid's team, though.
I do have a few questions though, Inane. Who writes the battle post? I'd assume the victor, but if there are multiple people on one team, who ends up writing? Also, where do we fight? Do we have background to explain the encounter? Or just fight? Personally, I'd want to fight in a high-tech arena, that we I could choose my battleground. And I'd have a roaring crowd to please.