How about you state who YOU think would win first, so we can just reluctantly acquiesce and avoid you getting all bent out of shape when someone disagrees with you?
Now now. I am all for debate if knowledge is obtained in it.
I only get bent out of shape if you will if people say the same old facts and nothing is gained and it's clear people are just arguing for the sake of argument. There's no point in such waste.

But since you asked kinda nicely: I say Volgin wins.

Reasons:

Tifa has the definite speed and skill edge. Volgin is strong but still a brawler. See his little torturing of Naked Snake:
YouTube - Metal Gear Solid 3: Snake Eater - Greasy Freebooter

However, Volgin has the strength, toughness and suerpowers edge.

For strength:
YouTube - Volgin Shagohod Boss Battle

That armor wasn't even dented by C3 and RPG rounds. Volgin punched through it easily.

For superpowers, Volgin has 10,000,000 volts of electricity in his body. He has a forcefield he can raise to protect himself as well as shoot lightning. Plus his bullet trick:
YouTube - Volgin Firing Bullets

For toughness, see the Strength video...he was hit by lightning after being blasted by an RPG-7 and he didn't even fall down. It took well over 20 rounds of ammo exploding inot his body to kill him.

So, with his superior strength and the fact Tifa never showed she could dodge or deflect bullets like Cloud, I think Volgin would win. And then Tifa ends up like EVA...I hope she likes it that way.

Volgin is also gay, keep that in mind.
Someone doesn't remember Volgin taking EVA/Tanya to his room multiple times.