Which is better IDE or SCSI? The best answer is "It depends." IDE is the way to go if:
SCSI is the way to go if:
With a multitasking operating system, the CPU can request data from the hard drive and then move on to do other tasks while it waits for SCSI to return the data. IDE forces the CPU to wait until the data is returned to the CPU, wasting precious CPU time.
In a nutshell, IDE is easier to configure than SCSI. But SCSI is more efficient. SCSI is more expensive. If you only ever plan to add one component, then SCSI is probably unnecessary.