RESERVOIR SEEDS?? sour d

ive been hearing an awful lot about this sour diesel shit and i dont believe ive ever come across it , but i was led to believe that reservoir seeds had good if not the only real sour d arround now adays,
i plan on bying some and wanted to know if anyone can tell me whats the best sour d cross
is it alpha d or chemdog double d??

nyways please help??