Depends, I don't know a shit about Vash so I need more info, but some facts about Revolver.
He can draw his gun in a split second, he never seems to miss either, he killed 6 men (with AK's) in the matter of seconds, and that is while having his revolver lying on the ground before shooting. He is damn fast and that could be his victory unless I'm missing something here....
Necessity is the mother of inventions.
(Don't be a pig, get an Icejaw sig.)
He is in fact extremely intelligent, has god-like reflexes, perfect muscle control, blurring speed over short distances and is superhumanly agile, demonstrating the ability to dodge point-blank bullets on several occasions. He is an unrivaled gunman who seeks to preserve life wherever possible. Vash exaggerates his foolish characteristics to make people feel unthreatened and to hide his identity (Vash's reputation as "The Humanoid Typhoon" is legendary, as is the damage and destruction associated with his presence). In fact, Vash shows complete focus and control when the chips are down and when he is attacking. His gun resembles a Mateba Autorevolver because of the lower barrel alignment but, according to writing on the barrel, fires .45 Long Colt ammunition like a Single Action Army. The inscription on his gun reads: "EF Auto Ejecting Double Action." However, Knives may have modified the barrel before he gave it to Vash.
If it ever came to it he would kill him. Vash may be soft hearted but i'm sure you seen him when he's mad? He's a beast wiped out a whole town and forgot his memories but still will kill if it came to it. It's most likly gonna come to it.
Gotta say vash. but i am curious where you got the idea that vash has TWO revolvers. the black revolver is knives's, but in any case vash would win simply because he can dodge bullets by calculating tthe trujectory of the bullets just by seeing where the gun is pointed, just like he did in ep. 3 i think it was, may have been number 4.