Personally, I want a lower guard on any self-defense or fighting knife. A guard serves two purposes. The traditional one of protecting your hand if you have to block steel-on-steel. And the less obvious, but more important one of keeping your hand from slipping forward onto your own blade during a hard thrust.
I am willing to consider designs with other "hand stops". Deep finger indentations and other grip features can serve the same purpose, if not usually quite as well as a guard. Still, that eliminates at least 90% of the folders that are usually recommended for self-defense as far as I'm concerned.
My other requirements are a strong and reliable lock, a secure grip, a point capable of efficient penetration, an edge with enough belly to enhance slashing attacks, an overall blade geometry and material tough enough to withstand the stresses of combat, and a deployment system that allows fast and certain access under stress. I will also take as long a blade as I can get away with.
The last considerations are legallity and practical carry, both of which work against most of the other criteria for a fighting knife, particularly length.
Where all that leads me is to the various folder designs that have flipper-openers which become a guard when open. My hands-down favorites are the Camillus Aftermath and Maxx Bowie. You can't really do better in a fighting folder.
If you can't get away with a 5-1/2" blade where you live, find out what the size limit is and pick an appropriate model with similar characteristics. The Camillus Dominator or Heat are my favorites in the sub-4" range. If your limit is 3-1/2" consider the Kershaw Boa. And there are similar designs in even smaller sizes if that's what you need.
--Bob Q