Favorite: Anaconda -- it's SO satisfying on the rare occasions that I pull it off?
Best: Triangle -- because of my short, stubby legs, I've had to get into the habit of angling and underhooking the leg. As it turns out, that's a great habit since it saves you from slams and allows you to do the Ryan Hall triangle finish.
Worst: D'arce/Brabo -- I want to be able to do these SO bad, but I just can't seem to get it right.
Oh, as for the guillotine, it's absolutely not true that just anyone can do it/it takes no skill. As someone else said, it's not just about yanking backwards...
Though I'm sure there are more, there are two technical ways of doing the guillotine that I'm aware of. One is to try to curl with the choking arm, rather than to pull with it. You try to bring your fist to your shoulder and that elbow to the hip.
I couldn't find the one where Kesting explained the part I'm talking about, but notice how he always curls himself laterally, as if he's trying to touch his elbow to his hip?
The second technical/efficient way that I've learned (from Josh Grispi's gym, actually) is to pull their head a bit off to the side as opposed to letting it be against your body. Your forearm will be parallel to your shoulder line, as opposed to diagonal. From there, you just extend your hips.
With each of these, it's important to keep your body curled forwards and your chin on his shoulder.
The guillotine is not a caveman technique, and anyone who approaches it as such won't be able to land it on anyone half-decent.
Highly opinionated but out of touch with the current MMA scene.