Poll
25%
63%
0%
13%
Vash's Angel Arm takes forever to charge up and fire.
Gene's caster shells aren't 'bullets' - they're casings for 'magic spells' that I'm sure can hurt Vash just fine. If Vash tries to charge his Angel Arm, Gene can simply take his shot.
Otherwise, if Vash simply sticks to his standard gunplay, he wins. Unless Gene stays out of the fight and gets the drop on him with a caster shot.