We study the optimization of exact renormalization group (ERG) flows. We ex
plain why the convergence of approximate solutions towards the physical the
ory is optimized by appropriate choices of the regularization. We consider
specific optimized regulators for bosonic and fermionic fields and compare
the optimized ERG flows with generic ones. This is done up to second order
in the derivative expansion at both vanishing and nonvanishing temperature.
We find that optimized flows at finite temperature factorize. This corresp
onds to the disentangling of thermal and quantum fluctuations. A similar fa
ctorization is found at second order in the derivative expansion. The corre
sponding optimized flow for a "proper-time renormalization group" is also p
rovided to leading order in the derivative expansion.