If you are looking for a knife for self defense, then deployment speed is crucial. I would recomend a small dagger, spear point, or clip point fixed-blade, with a sheath that can be attached to the belt so that the knife rides high. Make sure that the handle fits well in the hand, and provides a secure grip. A fixed blade is ready as soon as you draw it, and therefore is faster than any folding knife.
If you absolutely must have a folder, then get an OTF auto with a relatively narrow blade. Double action is probably best. Make sure the knife has a grip-tape surface, or finger grooves, so that it does not slip during a stab. The knife should fit your hand, so that it is in a comfortable position every time you draw it. An OTF is better than a manual because, when a situation arises, you can conceal the knife in your hand with your thumb on the button. If you are attacked, the blade goes from closed to open-and-ready in half a second.
If carrying an automatic knife is frowned upon where you are, then you have to go with a manual opener. A thumbstud is fast, but the knife must open smoothly. A narrow blade is best.
A balisong is not practical, even if you have experience opening them. Balisongs have straight handles and can become slick with sweat, which may cause your hand to slip onto the blade during a stab.
Just my opinions.
TheSurvivalist