Which is better for self defense?

I own a knife and mace, but I want a taser too.
Taser
Mace/pepper spray
Knife/switch blade
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For everyone say a gun, I do want a gun but that requires a lot of time and more money than I can spend right now. I will never buy a weapon as lethal as a gun until I can use it properly.
Which is better for self defense?
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