i like this fight! but it's a hard one.
dante is an incredibly skilled and powerful half demon half human. he has the ability to change his form to a powerful demon with enhanced everything! he's got heaps of awesome and useful weapons and the guns are just overkill. he can get stabbed, crushed, shot, electrocuted, thrown in lava and even off a building!
but sephiroth is a whole different story. the strongest soldier ever known, radiating with mako energy and an insanely powerful and long katana with the ability to cut through buildings and easily deflect greatswords. he can move extremely fast and can fly even faster.
both have an immense mastery of swords. dante has plenty of different swords for any situation and sephiroth has his masamune. they are both incredibly agile and fast but sephiroth can fly in his normal form which gives him a slight advantage. dante has guns and lots of them, and i'm not sure if sephiroth can deflect bullets.
you guys might not like this but i can't help comparing dante to cloud. they are both just as strong and both wield a giant sword. they are both capable of the same feats like running up buildings and matching sephiroths sword skill. they have both been stabbed and can both get back up and continue fighting. cloud has his mako powers like his omnislash v6 (as seen in advent children) but i think dante is a little bit stronger with his slightly smaller and lighter sword, his slight advantage in agility and his devil form is a bit tougher than cloud.
i'm going to give this one to dante becuase his sword skills are just as impressive as sephiroths and dante is just as fast. he's even faster and stronger in his devil form. also he has his guns which give him a great advantage in the battle.
i think dante wins!