I have been buying SpyderCo's since they first came out and no one knew their name. I never considered them a fighting knife. Great EDC and special purpose knives but I do not buy them for defensive use except for the Matriarch 2 which is a slashing, rather than stabbing knife. I also have the original Police model. My problem with them is that with slick hands, like blood, you hand can slide off the grip and onto the blade when you stab. You may hit a rib and next thing you know, you have sliced your hand open. As any ER people you know what a tell tale sign of stabbing someone is.
I prefer knives with a hilt that prevents your hand from sliding onto the blade or in the case of my Jim Wagner Benchmark auto knife, finger groves like you find on a gun. Given the large odds that the knife will be used just for every day purposes, a Spyderco is a good choice. Quite honestly, as someone who has some custom made and expensive knives, my inexpensive knives do a great job of everything I need them to. My favorite is a Leatherman Folder. Been using it almost every day and it is still sharp and sturdy. My best defensive knives are:
http://www.blackhawk.com/Products/Accessories/Knives/Folding/CQD™-Mark-II™-Type-E-Manual-Folder.aspx
and
http://www.blackhawk.com/Products/Accessories/Knives/Folding/Be-Wharned™.aspx
The Be Wharned is essentially a heavy duty razor blade. I have cut myself a few times just cleaning this one. Very sharp and a great slashing knife and good for opening boxes and letters.
Another favorite of mine which is just mean looking and will cut to the bone is:
Spyderco Matriarch 2
I always have a small SpyderCo LadyBug on my key chain which takes care of my every day cutting needs. I also wear a neck knife at times but for defensive I take one of my serious blades with me. Any knife can be a weapon in the right hands but the problem is that less people take training with knives than do with guns.
What I have done lately is just carry a 5 oz. NAA Pug in .22 mag instead of a defensive knife. I do not have to get close to use it and it is smaller than any of my carry knives. Then I can slip a small knife like a Delica into my pocket for normal needs. Neck knives are nice. I have a few. Sometimes you are in a scuffle and cannot get to your pocket and that is when your neck knife comes in handy.
For serious use I carry my Cold Steel Tanto. It has a very sticky rubber grip and can penetrate a car door without your hand sliding over the blade. It is the original model with the good steel. I forget all the steels on my knives; too many of them to remember. My favorite of all is my Vietnam knife. More like a dagger with a nice handguard. It is essentially the Gerber MKII with serrations near the hilt supposedly for cutting into kidneys. Mine has a slightly curved blade. It is curved so that when you strap it to your leg, it conforms to the shape of your outer thigh and holds it close. For me, it is a perfect fighting knife along with the popular
Applegate-Fairbairn. If you wear un-tucked shirts, concealing a knife is easier than concealing a gun. They even have shoulder holsters for knives.
If you are just looking for a get off me knife, anything with a sharp blade will do. If you intend to fight with one, I would consider a different knife. I have lots of folder and non folder knives to choose from so I like to mix them up like I do with my guns. These days I often just carry my NAA Pug in .22 magnum. While it cannot cut (unless you put a bayonet on it and they do sell one), it is a great get off me weapon without having to get close to your opponent.
Here are the knives I carry for defensive use. I have a SpyderCo Lady Bug on my key chain and it handles most of my cutting jobs.
http://www.blackhawk.com/Products/Accessories/Knives/Folding/CQD™-Mark-II™-Type-E-Manual-Folder.aspx
http://www.blackhawk.com/Products/Accessories/Knives/Folding/Be-Wharned™.aspx
https://www.spyderco.com/catalog/details.php?product=719
https://www.boker.de/us/pocket-knife/boker-plus/tactical-knife/01BO048N.html
If you are just looking for a knife that will probably never be used for defense, than any good blade will do. I have very expensive knives and the one that I use daily is made by Leatherman. It is very light and still has a sharp blade after 5 years of daily use. You cannot go wrong with Spyderco. I keep their original Police model in my car and have most of their original line of knives which I will someday sell on ebay.