or maybe someone could point me in the direction of the thread that this has already been talked about?
That's why we have a search function
Knives as a self defense weapon is a poor idea. With a folder you have to worry about getting it out and opened without dropping it, then once it is opened you have to worry about not letting go of it.
Fixed blades, while you don't have to worry with opening them, you do have to worry about getting it out of a sheath. Same with neck knives, but then you have to fish it out from under your shirt.
My opinion on self defense is this:
Learn to talk your way out of a situation or give the bad guy what they want. Most muggers aren't intent on hurting you, they just want your money. Introducing a knife will just put them more on edge and turn on their defensive mechanism.
If talking doesn't do any good, just run. Your feet are the best self defense tool you've got and no one has to teach you how to use them. If running doesn't work then you've always got fists.
For people who are truly paranoid about going out of their house unarmed (and I feel sorry for them), if you live in a state that allows concealed carry of a handgun, then by all means get a gun. Just be prepared to kill whatever you point it at and live with the consequences.
I carry two knives every day. One for food and one for whatever else needs cutting. Only once have I ever opened a knife in a sticky situation and that was to protect someone I loved, not myself. I know how to take care of myself without resorting to weapons, but all bets are off if you threaten someone I care about.