Using the ignition method may cause unburnt fuel to pass along to your catalytic converter, and may reduce its lifespan. However, cutting power to the pump will result in a slower kill, because fuel rail pressure doesn't drop to zero instantly. It may take a few seconds for your engine to die, and in those seconds it will probably lean out significantly.
I'm currently using an injector kill.
EDIT: Aerodynamics seems an odd section for this question.
