Scout and Blitzwolfer
My reasoning is scout would have been trained in the plumber academy so would be affective at hand to hand combat and the omnitrix will always turn Ben into the prime of each DNA so the his Loboan form would be at it's prime which is why 10 year old ben was able to be on par with the Yenaldooshi and ben would have more experince after six years so for me blitzwolfer and scott would win in a landslide