The Pent D suites me fine. But others would like the X2 From AMD. They have charts to prove that the X2 is faster than the Pent D line because of their chip structure, and the way AMD made [EDIT Designed it] it. Intel, from what I hear, rushed the D line into the market. So overall, right now the AMD X2 line would be the best choice because of the way the chip is made [EDIT Designed ] , and because of it's core. Unlike the Pent D, which is made up of two Prescott cores, which these days, run very hot, which is bad for performence.
From AMD Tech.
I'll give you more graphs.