Best how?
Best price/performance 955. Best 4 core 980. Best 6 core 1090T or 1100T, haven't a clue. Best 6 core price/performance 1055, from reports.
Best reasonable purchase, lowest priced 3 or 4 core under $100.
Basically the top ugrade is the 955, best sub $100" deal probably the Athlon II X3 450.
Spending more go I3 2100 or wait for Bulldozer.
For all that, my on sale purchases 635 and 925, YMMV.