I'm not a huge fan of mounted lights on pistols, however, if the light is detachable - like the M3 - then you at least have the option of using it either way. But, I like the idea of having a momentary switch on a combat light and not having to point my gun at everything I need to illuminate, so I go with the Surefire's. I carry a Aviator A2 with me everywhere I go.
Like most things gun/self-defense related, there really is no perfect answer. So we do our research, make a choice and then train, train, and train some more with it.