Why do you need to remove it? Are you putting on an aftermarket one? You won't notice much of a difference. Unless it is broken then I would leave it alone.

Anyways, to answer your question, an impact would work best. If you try to do it by hand the engine is going to want to crank and you'll have to improvise and think of a way to keep it from turning. With an impact, it zaps it off before the crank even knows what happened. Be sure not to lose or misplace the key.