A general rule of thumb is low crit chance should be offense. However, the actual break point can fluctuate, as the offense set benefit is mitigated by offense from mods and unequipped gear (the bonus only calculates off of base offense), and the CD set benefit can be effectively reduced from additional CD bonuses (leaders, uniques, buffs, stacking CD). It's actually possible with enough CD bonuses to get more benefit from an offense set even when CC is 1. But this can swing the other way again if your offense from mods is extremely high.
So you can extend the rule of thumb to this: Offense when CC is low or you have a lot of additional sources of CD, or CD when CC is high or you have a lot of offense (primaries and secondaries) from mods.
