Rate each of these by priority:
Price
Speed
Reliability
Pick 2
Seriously though, I generally go with SCSI for servers because SCSI hard drives are typically more reliable than IDE. However, you can almost do IDE RAID 0+1 for the same price as SCSI RAID 5 and the performance of the IDE RAID 0+1 would most likely be better assuming you use 7200RPM IDE drives and 10K SCSI drives (If you used 15K SCSI or 5200 RPM IDE, the SCSI would be faster.) SCSI RAID 0 is going to be faster than just IDE RAID 0 assuming you use faster SCSI drives, but the IDE RAID 0 is going to be a lot cheaper.
If this isn't mission critical data or your backups are frequent enough that it is an acceptable risk use RAID 0 (striping).
The biggest advantages of SCSI over IDE are that one can obtain higher RPM SCSI drives and SCSI drives are typically more reliable. IDE is a lot cheaper and the fastest SCSI drives do not hold as much data as the largest IDE drives.
If you really care about uptime (i.e. 99.5% uptime) you probably want to run either SCSI RAID 5 (with a spare disk), IDE RAID 0+1, or SCSI RAID 0+1. You would also want an enclosure with redundant SCSI busses, power supplies, and controllers. Then you would want to put it all on a UPS.
In other words, give us more info on exactly what you want.