I would again point out that I am only discussing this issue philosophically, and I mean no disrespect in any of my answers, but here we go again:
To score a critical hit with a combat knife is not difficult. Legs, achilles heal, hamstring, thigh, hip, groin, stomach, chest, lungs, back/lungs, biceps, triceps, forearms, hands, fingers, neck, and head will all severly injure an opponent, cause loss of blood (a persons' own blood loss has a significant psyhological effect in a fight), and decisively win a hand-to-hand fight.
Legs, thighs, biceps, triceps, forearms, hands (to a certain degree) fingers and even head wounds will not put an immediate stop to most hand to hand fights, and even a penetration of the stomach or kidneys won't guarantee a stop. I have been variously injured in all those areas, to include playing a full season of football with a torn biceps, and none of them would have kept me out of a fight. Hey, I actually got SHOT in the kidney, and while it sucked horribly, I wasn't out of the fight for a good couple of minutes. That same gunshot tore a hole in my stomach too. Keep in mind that I don't mean to make it seem like it's impossible to disable an enemy with a knife, and I understand that getting cut sucks, but in the long run, it's still just getting cut. Frankly, a hard enough punch or kick to the groin will cause enough immediate pain to disable an opponent as getting stabbed there will.
Incidentally, you do bring up an excellent point about seeing your own blood, and that is if your planning on getting into a knife fight, you should also plan on getting cut up, a fact curiously overlooked. You must also realize that to execute many of these moves requires you to be in very, very close and if your in that close, it's not as if your opponent is just going to stand there and let you shank him. if your opponent happens to trap your stabbing arm (which, incidentally is where all his attention is going to be), your pretty much out of luck.
A club isn't the perfect weapon, but it has the advantages of creating distance, being exceedingly easy to use, and creating signifigant amounts of pain across a relatively wide area. Also, by very nature of physics, your going to be transferring much more energy into your opponent with a club than with a knife. For example, a downward slash with a knife that is blocked by an arm is, at worst, going to result in a lacerated arm. That same sequence of events with a club is likely going to break that arm. You asked if I would rather go into a fight with a knife or a club, and 100% of the time, I would answer with "club". If you stick me in the forearm, I am going to feel pain in that specific area. If you whack me with a club, I am going to feel pain across the breadth of the strike.
Honestly, if I had to use any hand weapon in a fight, I would use a spear or a halberd. I don't know how to use either, but for all the talk about how awesome swords are, halberds were for all intents and purposes the kings of the battlefield, and it's because they created space.
As a final aside, when we were deployed to Somalia during Operation Restore Hope, you know what our best weapon was? The axe handle. The Somalis figured out pretty quickly that we weren't likely to stab them and that they weren't that scared of getting stabbed anyway, but they were quite afraid of getting hit with an axe handle. We had our rifles, but stupid rules of engagment meant that they were useless most of the time, and so axe handles became the rule of the day, and they worked very, very well.
