basically s754 is meant towards mainstream while s939 is more towards highend. Nowadays they run about the same price so I'd recommend s939, with s939 you will have better ability to upgrade in the future and the dual channel memory helps in some programs by alot.
Watch out for the <b><font color=red>bloody</font color=red></b> Fanboys!
AMD64 2800+ :: MSI Neo-Fis2r :: 1024mb Kingmax ddr400 :: Sapphire 9800pro 128mb :: 10K WD Raptor
Addicted, finally.