Myotismon is a fierce Digimon who has many super forms. His abilities only seem to grow with each new incarnation, but he is not yet at the level where he can hope to stop Vegeta. Vegeta can end the whole galaxy in a single shot. There’s also no attack at Myotismon’s disposal which could cause him any significant injury. As such, victory is all but guaranteed for the Saiyan. Vegeta wins.