A discussion about ninjas?!?! -Kaination jumps to save teh day-
Here's my simple logic.
Ryu moves so fast. The prince goes and stops time. But since Ryu is a ninja, he just merely slows down, cause he's that fast. Then the prince would be forced to use kick ass combos, but Ryu just dodges him and throws 300 consecutive ninja stars. Luckily, since time has been stopped, the prince just barely managed to dodge the ninja stars, and as he thinks of a quick plan. he uses the daggers to move back time, to the point where Ryu starts throwing the stars, and once he begins, the prince quickly jumps to the side and dives at Ryu. Ryu, not knowing how he could of possibly predicted that, did a back flip and landed on the ground. They stare at eachother.
Immensively
Ryu quickly realizes that the daggers are causing time shiftments in the quadratic vortex we know as time. Ryu quickly dashes and cuts off the arm holding the dagger. He lunges and grabs the dagger, and swiftly jumps back and holds the dagger in the air and shouts, "SLOW TIME!"
BUT ALAS! That dagger was just a novelty toy found in McSpetterson's toy shop on 1523 McHenry avenue. The real dagger was in the prince's side the entire time!
The prince uses the last of his sand power from his real dagger to completely stop time. He walks up to Ryu and spits in his face, and completely decapitates him. The prince resumes time, he walks off, with a great grin on his face. Then, he heard a big poof behind him, and as he turned around a log was in place of Ryu. Ryu quickly jumped from the cieling and cut the prince in half.
Winner: Ryu
It was one hell of an epic battle
Ya, i havent played ninja gaiden and only prince of persia one, so my answer might be a bit vague D:
But, since Ryu is a ninja, my vote goes to him.