Is this even a question? Anderson Silva.
Others have had success using knees, but few have had that kind of success against that kind of opponent. Franklin x2, crippled Leben with knees, broke Bonnar, broke Chael, sent Newton into next year.
Second place has to be Aldo. That KO on Swanson, the knee on Perez, and of course the Mendes KO. Goddamn.