Sean O'Malley had a good record both in his Amateur Career that has 9 fights that only has 2 losses and on his Mixed Martial Art Record that now has 12 matches, even though he is just a recent fighter on UFC I think he fits the bill for a shot for the belt in the future.
Marlon Vera is the toughest opponent Sean O'Malley is facing in his career and his two losses in the amateur bout was by submission and Marlon Vera does have some slick submissions and never lost a fight by knockout. I am going with Sean O'Malley because of his striking skills.