Apparently clawhammer is available for socket939 cause thats what CPU-Z says mine is. But yeah clawhammer cores are 0.13 micron and the newer San Diego and Venice cores are 0.09 micron. It's better to have a the 0.09 core, although it isn't that much better than the 0.13.
Clawhammer was used for Socket 754 and Socket 939 back in the old days when the very first Athlon 64's came out. Perfect museum quality.
San Diego is the newest core available. They are designed for Socket 939 and uses an enhanced memory controller compared to that in the old Clawhammer. San Diego also uses a smaller manufacturing process of 90nm instead of Clawhammer's 130nm for a faster and efficient chip.