Are you talking knife training or straight up self defense? For the knife, any of the filipino martial arts systems are nasty with a blade. Joe Blow with a knife is bad news...being trained with a blade is d-a-n-g-e-r-o-u-s!!
For general self defense, i say Brazilian Jiu Jitsu...some folks will disagree, but I think the mechanics are just brilliant and nothing gets you up and running faster.
The problem with Brazilian Jiu Jitsu (and some other ground fighting arts) is that they tend to focus one on one, which is great unless his buddies are kicking you in the head.
I remember being a white belt (Aiki Jiu Jitsu) and taking apart a 2nd degree black belt (there black belt was Gojuru Karate) while sparring quite easily. He had spent the last 10 years learning a martial art that was based on katas and no real physical contact, while I had spent the last 10 years mis-spending my youth.
Even among the same martial art there are differences between schools in what they specialize in.
Tournament Hapkido is much different then combat Hapkido asan example
