Lelouch's Geass is set up to where he makes eye contact with his victim and whatever command he gives and all the other little details he gives, his victim must follow it to the letter, no matter what command and the victim can possibly not remember doing it depending on what it is. However, Lelouch's Geass only works once per person, maybe twice since he ends up getting a dual wield.
For KA, it's subtle mind control where the user subconsciously gives in to the commands of the user without knowing it. KA can be broken when the victim is a aware of the control. KA also seems to have a huge amount of time where the eye must recharge for another use unless you have Hashirama's DNA.