What's your crit damage?
You can calculate it out to decide which is best.
final_damage = (base_damage * rand(0.95 to 1.05) - armor * (1 - armor_penetration))
* (ability_multiplier)
* (1 + critical_damage_bonus + flanking_bonus)
* (1 + attack_bonus + damage_multiplier + type_bonus)
* (1 - magic_resistance)
critical_damage_bonus = (crit_chance)(crit_bonus)
Let's assume 100% crit damage and base damage of 80, to make it easy. A crit damage of 100% with 45% crit chance is a critical_damage_bonus of ((.45)(1)).
All else being equal and ignoring the random -/+5%, your baseline average damage without rings would be:
= (80)(1 + (.45)(1)) = 116
With two Rings of Slicing (assuming they stack both crit chance AND damage, which is a big assumption):
= (80)(1 + (.55)(1.2)) = 132.8
With two Superb Rings of Attack
= (80)(1.20)(1 + (.45)(1)) = 139.2
Seems pretty clear cut that boosting crit chance AND crit damage is the loser, based on these assumptions. If your crit damage is lower than 100%, run the numbers again with the correct crit damage. For example, if your crit damage is only 80%, then replace (1) with (.8) and (1.2) with (1).
The break even point is left as an exercise for the reader. 