*Edit: I get the impression you mean which game has the biggest swings. Variance is always going to be the same. The math behind an 80% favorite doesn't change based on the game. Any talk of variance in the rest of this post is really talking about swings, which is determined by standard deviation.*
In general no matter what game, the fewer the players the greater the variance. HU is most volatile, FR the least.
Any NL game is higher variance than PL, which is higher than Limit.
It's hard for me to say which form of poker I think will be the highest variance. Hold'em and Omaha are both up there. I would give this to Omaha if it had a NL variant being played, but since it does not, I've given the #1 spot to Hold'em.
After that I'd go to Omaha, Stud, Omaha8, Stud8
I have no idea where Razz fits in, as I don't play it, but I'd wager it's in between Stud and Stud8.
The trick of this, is that in all honesty it doesn't matter what game has the most variance, because variance isn't something to avoid. If you can get players in with hands that have little equity and they make their hand so be it, that's great! That hand will likely contribute to their continued poor play in the future, and you got it in good.
A very good HU NL player, which based on this crude ordering is the #1 most volatile form of poker, isn't going to bemoan the fact that variance is intrinsic to his game. He's going to have a lot of ups and downs, but overall will do quite fine for himself, because if variance really is to blame, then he's been exploiting his opponents, getting it in ahead, and continuing to do this will result in a profit.
I would suggest playing a game that you are interested in. Focus wholly on bettering yourself in that game, and you will be much better off than searching for less volatility.