So Hephraak is kind of a special case for this one because of his passive Counter Attack.  Often hes built with 100% Crit Rate for that, even though he has the self buff.

Generally otherwise id say build at 70%.

I built my Hephraak at 70% CR even though he might counterattack w/o the CR Buff.

Most newer toons have 3 turn CDs on their skills and the CR Buff usually last for 2 turns, so the only exception would be a toon where you want to Crit on every A1, in which case, you'd need 100% CR.