Vash wins. His bullets can make blackholes in the manga and Jack, from what I've seen, is barely faster than Vash so a blitz is out of the question. Plus Vash's reaction speed should be greater than Jack's considering that he dodges bullets, and not just aimdodging, but actually dodging (he dodged a sniper trying to kill him). Also he dodged barrages of heavy machine gun fire from multiple experienced gunmen. The only time he has been hit by bullets was by Knives, but that's because Knives is practically equal to Vash in gunslinger. Vash is also a master with guns. He makes the Punisher look like an amateur. Even with regular bullets he can take this. In reality, Jack's Sword wouldn't be able to hurt Vash due to Vash having a Goku type heart. But since we always set it that it can, it will here. Either way Vash wins.