My vote is the AMD Athlon II X4 620 Propus. Many people are able to OC it passed +3.0ghz w/ the stock HSF and voltage. Also, it has one more core over the Athlon II X3 435 Rana. That can't hurt
However, some people are able to "unlock" the 4th core on the Athlon II X3 435 Rana. Depending if your mobo supports the ACC function, I believe. It can be overclocked well passed +3.0ghz as well.