By no means would this fight be quick, but GoWII Kratos takes the win here. Sephiroth in AC was close to a God-level being. IMO, Kratos was closer with his weapons, spells, and overall abilities. I actually was not as impressed with Sephiroth's speed in AC as I was with someone like Dante's. The Masamune is known for being an unnaturally long sword, but Kratos undeniably still has a range advantage with his Athena's Blades (they're practically twice the length), and he wields them with alot more speed than he's given credit for.
Sephiroth has jumping ability that can pretty much be called flying--Kratos fought at least three things that were in midair in God of War 2 (Icarus, Lahkesis, and Atropos), all of whom he owned in verying amounts of time all three of which was while he was in midair. Besides, there was at least one occasion where Kratos performed a pretty impressive leap himself in GoW2 (when he was escaping the Colossus of Rhodes' body after absorbing all of its power with the BoO, he jumped out of it's mouth and leapt a big distance off of its arm). But if Kratos needed to fly or jump massive heights with finesse to stand a cahnce against what he'd defeated, then he'd've been mincemeat on his journey after three minutes on the Pegasus.
Kratos' spells in God of War 2 are also enough to at least equally counter Sephiroth's assault in almost any proximity. Too close, Cronos' Rage (almost undodgeable up close, and can last a long enough time to give Kratos). Too far, Typhon's Bane (rapid blasts which can home in on Sephiroth, and don't forget the whirlwind). All over Kratos, Atlas Quake (dozens upon dozens of boulders flying off in every direction should at least throw off Sephiroth a little bit, I don't see it finishing him off though).
Power isn't limited to just physical strength, and we have yet to see the limits of Sephiroths physical strength anyway. When Kratos has the ability to stop a planet threatening attack with his mind power alone, then he can be considered competition to Sephiroth in terms of power.
It is a feat in terms of power, it is something he accomplished as it was part of the story, just like how Pyron has absorbed a planet, its not a "battle" feat, because we don't see him doing it in battle, but its still a feat of power itself..
His willpower is his power, his magic is his power, the negative lifestream is his power, its his abilities which make him "powerful" thus making him more "powerful" then Kratos.
Until I see Sephiroth or Azul the Cerulean pull the main head of the Hydra onto a mast or toss the Colossus of Rhodes on its ass with their bare hands, I'm not gonn a say that they're strength is at the level of Kratos'. Sure, we can presume Sephiroth has superhuman strength, but every feat of physical strength in FFVII is nothing Kratos can't/hasn't done or surpassed. Yes, Sephrith can summon the lifestream with a gesutre of his hand, but the Blade of Olympus can summon a mushroom-cloud that spans throughout the entire landscape that will banish any of its targets t othe darkes pits of the underworld, by being struck into the ground. Need I say who has the Blade of Olympus?
Sephiroth is FFVII's most powerful being in the series, a series that involves a stylistic emphasis on combat with plateus of power that in all reality don't reach towards the levels beyond its own planet. In God of War, we have a series where the main character, though presented more grisly, is a man whose overall power rivals that of the rulers of that entire universe, and is currently on the verge of overthrowing said rulers.
Technically, we never saw what he did to it. That, and the Midgar Zolom was barely half the size of the Hydra, who Kratos did the exact same thing to.
You mean the leader that endured about FIVE impalings after a battle at the world's summit, and the Athena who was killed with one stab by a weapon that's actually more powerful than just a five-foot hunk of steel? That, and Sephiroth was hardly "fine" in the technical sense, he may have been alive, but barely and probably wasn't gonna last much longer had he not been thrown into the life-stream. Besides, it doesn't speak well for his awareness levels (at his weakest state), having been snuck up on by a 16 year-old Shinra grunt.
I still don't see how Kratos would beable to escape Sephiroths willpower, as it did hold immobile a power that is powerful enough to threaten the entire planet, Sephiroth is also much faster, and even if Kratos can simply summon the Cloud, he has to strike it into the ground, Sephiroths willpower TK works on a thought, which is faster, and with a simple gesture his NL is summoned as well.