Are there bets that are "better or worse" when it comes to variance?

The variance changes according to how many numbers you bet.

Var = n * p * q (p = probability of win, q = probability of loss, n = number of trials).

You can find the turning point by calculus. Because q = 1 - p the variance is Var = n * p * (1 - p) = n * p - n * p^2

The variance curve for a binomial distribution is a quadratic with the minimum at the bottom.

To find the min value of p set the derivative of p to zero. n is a constant so is taken outside the differential operator-

n * dVar/dp = n * d (p - p^2)/dp = 1-2*p

set equal to 0 and solve for p

1-2*p = 0

p = 1/2 , so the bet which has the minimum variance is the even chance.