What it likes will depend on a lot of variables like CR, quench, combustion chamber and cam timing/events. (Edit: I see Andy beat me to this..)

Mine likes 36° total on 91 no ethanol. Starts INSTANTLY and shuts off easily. That goes away when I pull 6° out for the nitrous. It is harder to start and doesn't like to shut off without running on. Eventually I will put a timing adjust knob in it for the MSD but for now I am doing it manually.