That would be a difficult one to decide (Good topic though).
On one hand, you have the Nine-Tail Demon that's inside Naruto. He could crush enemies with that.
On the other hand, you have a half-demon that uses a sword that gets uber bonuses when fighting other demons. Not to mention it unleashes a counter attack, where its power is directly proportionate to the power of the attack coming at him. So the more powerful the attack, the more powerful the Tetsusaiga gets.
If Naruto could disarm InuYasha (it's been done), then the fight would go in Naruto's favor. Otherwise, InuYasha would have a very good chance of winning.