SCSI is by far the best and fastest if your looking for speed, its all I used to use (untill recently) on my web and video servers. The one I used was the seagate Cheetah (
http://www.seagate.com/products/discfamily/cheetah )
SCSI drives are louder then IDE drives, they sometimes sound like they are falling apart but I have never had one go out on me.