I think Glacier shall be better as you wanted sth for backup. Some data that is just going to sit there needn't be costing those many dollars as it would cost you with S3. Reliability is all the same for all practical purposes. I am waiting for a Glacier client that saves my data in some format that I can read with any other client with the same key. Arq is Arq-to-Arq only.

Another option is CrashPlan. Been using it. You can have Glacier with CrashPlan too. It's that cheap.

How many GBs/TBs?