Random

David Campbell-Ninja Warrior All Star.

Ryan Stratis-American Ninja Warrior.

Facts
David has been in Japan many of times & he was close to the final Stage. Ryan is a US Army Athlete who is in all three seasons of American Ninja Warriors.

X Factore
A Ninja vs US Ninja thats not random. 4. Wins-David's was in Seasons 1-3 thats 3x10=30 & Ryan's Results in 3rd season 1:03.15+3:22.21+1st Semi Finals+13.97+18.41+4
 * 1) Weight/Strangth-David is havy than Ryan but Ryan is Strange. (160/145).cm
 * 2) Brains-Thir Brains are about the same. (52/52)%
 * 3) Speed-David & Ryan are probley the same. (170/170) M.P.H.

I think the Daedliest Challenger is Both!
Becuse their both are Warrior of a live time. But you can vote your Challenger on comments.