I agree with LCGuy on this.
If you really want to stick with just SCSI or 1.1 I will warn you that there are tradeoffs of each. I find USB 1.1 to be painfully slow, even when using flash-based products such as older USB memory keys. However, it is far easier to troubleshoot and configure than SCSI, which is like pulling teeth to say the least. It can be faster than 1.1 from what I've seen but if you are looking for something where you don't have to worry about termination or other issues I'd go with 1.1.
FireWire could be another option; LaCie makes some nice external drives for the bus.
If you really want to stick with just SCSI or 1.1 I will warn you that there are tradeoffs of each. I find USB 1.1 to be painfully slow, even when using flash-based products such as older USB memory keys. However, it is far easier to troubleshoot and configure than SCSI, which is like pulling teeth to say the least. It can be faster than 1.1 from what I've seen but if you are looking for something where you don't have to worry about termination or other issues I'd go with 1.1.
FireWire could be another option; LaCie makes some nice external drives for the bus.