IMHO, today SCSI only makes sense (and fits really good) in servers with heavy load. In normal desktops however, SATA is the best choice, clearly the most bang for the buck. SCSI is very expensive; the controllers, cables, terminators, the drives, everything is ridiculously expensive, and the drives are small (and often rather noisy) in comparison. It's tough to defend the usage of SCSI in desktops. If you want to, you can squeeze a little more performance from the SATA if you set them up in a striped RAID configuration, but then you should pay even more attention to frequent backups of your important data...
