Tasers are useful for cops because normally there's more than one cop on the scene. If it doesn't work they've got other options.
The dart shooting type may look good but there are too many thing that can go wrong.
The only one I'd recommend for for self defense is the direct contact type. Not ideal but it will work more reliably.
If I lived in the US and I felt my wife needed to carry I'd get her something like this
and take her to the range so she knows how to use it.
