http://www.youtube.com/watch?v=_A6jQulFXN0 nice find. that gave me teh chills at the end with him pulling on the neck crank like that!
The one that personally causes me the most pain *without* the submission having pasted the injury point is the bicep crank. Just nothing good about it.
I actually find it pretty painful when someone fucks up a blood choke and desperately attempts to submit you by just pulling on your neck as hard as they f*cking can.
I'm gonna go out on a limb and say that any joint lock can be excruciatingly painful if applied correctly. Obviously, the least painful would be an artery choke since you don't know you're really in trouble until you're on the verge of blacking out. That's pretty subjective though. They can all fuck you up but I would say leg locks. You don't really HAVE to use your arms to get around in day-to-day life, but every time you put weight on a jacked up leg you feel it.
Yeah I was about to say leg locks, there have been some nasty injuries from leg locks. Notably the victims of Masakazu Imanari especially MTB. Bas Rutten broke somebodys shin with a heel hook. Nasty stuff.
thats called a spladdle in the diaz vs stevenson fight!! but most painful would definately have to be any twisting style lock to the knee