ddr is the best, practically because of higher bus speeds and bigger caches......SD is **** unless you have a p1 that you need to boost...!!all p4's however either accept RDRAM on their mobos or DDR...
ive got two 80 gb Seagate Barracuda's and one WD 30GB Hdd...i used to have a Nikimi 40 gb aswell but it got ****ed after 6 months of running, the exact day when the warranty ran out.....