If it's for SD mainly, then something like the Large Ka-Bar TDI knife may be what you're looking for. Quite intuitive to use. On the other hand, in SD knives, you may want to consider the looks of the knife: if you end up using the knife, it's not going to look good in court if the knife is a blazing tacticool, riddled with mean-looking serrations and questionable slogans etched on the blade.
This is more a topic for practical tactical, but I wouldn't consider carrying a knife for SD without training a "really bad idea", unlike some other members. Training is great to have for any tool, but most people who have in fact killed someone with a knife did not have training for it. At least that is the case in my country. A knife is a very simple tool, and makes an equally simple weapon, that people have been using throughout history. Better to have a knife and no training with it, than to have empty hands and no training with them. Of course, it's much better than either of these options to have training with whatever you're going to be using, be that empty hand techniques or something that you have to painfully slowly draw out before using it.
Now, saying something like this out loud often invites the "if you have a knife and no training, they'll just take it from you and use it against you" argument. Quite frankly, that's one of the most BS arguments I've ever heard (and you hear a lot of BS in this country). First of all, if your opponent is so good that he'll just routinely disarm you just like that, then it doesn't matter what you bring or do not bring, you're going to get beaten anyway. If he takes your knife, so what? He probably already had a knife if he attacked you, possibly a firearm. The chance that he had no weapon at all is minimal indeed. So, how have you made the situation worse in terms of weaponry? Sure, you lost your weapon, but then, he already had one to begin with, almost certainly. Yes, it's true that drawing a weapon to defend yourself with may infuriate the bad guy even further. But guess what. Unless you can see the future, you don't know that. Maybe he'll get second thoughts and run instead, noticing that you're armed and not the easiest possible target - that happens very frequently in this country. Or let's assume that you don't draw the knife, and just curl up to a ball and surrender. How do you know that won't infuriate him too? Maybe he'll think of you as a worthless dhimmi that doesn't even have the courage to defend himself, and maybe he'll just kick your skull in while you lie there on the ground, not fighting? The fact is, you won't know until it happens.
But I digress, so I'll end my rant there.