Kitchen knives are usually not suited for defense.
The blades tend to be too thin and too narrow, and will often break if used for defense.
Kitchen knives need to be very hard to take and keep a sharp edge, and that can cause them to just snap if misused for other purposes.
Second, they have no cross guard to prevent your hand from sliding down on the blade.
A common occurrence in people killed with a kitchen knife is the user gets cuts on his own hand.
To be an effective defense tool a knife needs to be usable for slashing and stabbing.
There is no "best" blade for defense, since everyone has different ideas of what suits them.
Defense knives tend to have thicker, less breakable blades and some method of keeping the hand from slipping onto the blade.
Other then that, there are literally tends of thousands of "defense" knife designs.
One critical necessity is to get actual Real World defense knife use training.