Originally Posted by mizanation
there is a lot of speculation in this thread, but i've actually trained in most of the styles mentioned. i also compete competitively in submission wrestling and several of my good friends are pro and amateur mixed martial arts fighters (a.k.a. vale tudo, no holds barred, ultimate fighting, cage fighting, etc).
let me tell you first off, that physical conditioning is the biggest factor in fighting. if you are strong, powerful and athletic, you will have an advantage in a fight, even over a moderately skilled (but weak) opponent.
second of all, it doesn't matter what style you study, as long as they train full-contact with a 100% resisting opponent. what styles do this? boxing, wrestling, judo, bjj, mma, muay thai. it's no surprise that these styles are also considered the most effective martial arts. (notice i did not include krav maga and systema and other "lethal" top-secret special ops military styles)
third, to be effective in a hand-to-hand street fight, you need to cover all the ranges of fighting--striking, clinch and ground. for striking, boxing and muay thai have the longest history of proven effectiveness. for clinch, greco-roman and judo are two of the most effective in this range. and for ground, BJJ is by far the most effective. if you become proficient in all three ranges, you will be fine in a hand-to-hand confrontation.
lastly, and maybe the most important thing, no art will give you the magical skill of defending against a knife or a gun. any martial art that claims this is selling you a fantasy.
the best self-defense is awareness and avoiding dangerous situations. you can avoid 99% of dangerous confrontations.
I don't know about other "top secret" military styles, but I think that you have the wrong idea about krav.
basically - it comes down to different attitudes - you can get in fantastic shape, and spend 10-14 hours a weeks studying 2 or 3 styles, and get to be a fantastic fighter. or, you can find something that will fit in with a normal lifestyle and take up 2-4 hours a week of your time. the advantage of krav, and I think several styles that are usually called "combatives" is the relativly short learning curve for getting to a situation where you can do pretty good damage, as long as you aren't dealing with somebody who has been putting 14 hours a week in BJJ and MT classes for the past 12 years.
if you take 2 healthy and basically fit 18-30 year old men with no expereince, and give them some training, one in krav and one in a traditional style (or even bjj), for the first 200 hours of training or so the krav student should have the edge, and then it will flip over the the other guy.
nothing secretive - just krav has taken out a lot of the basic stuff that you use to build a better foundation, later on, that you may very well not need if you are fighting a person who isn't a master martial artist.
I did a 6 week krav course, about 20 years ago (on top of a few years of korean and akinawon striking styles, and about a year of judo). after 18 years of not practicing, I joined a typical american mcdojo and was able to put the fear of god into a room full of young fit black belts - who had been studying a style (or more acuratly a school) that discouraged practicing any type of real contact or realistic combat work.