Probably Nattie's Sharpshooter. But, I also like the Anaconda Vise, the LeBell Lock, Del Rio's armbar and the Ankle Lock. And if Morrison would have started using it, the Texas Cloverleaf would also be on the list.
The Lebell Lock. Although I wish more people would sell the omoplata as painful before he gets the crossface locked in, it'd probably make the move look TOO devastating. And to be fair, they have booked it really very well.