Earlier quoted context omitted.
My current backup is around 300 Gigs. I see the big advantage of Arq (over Backblaze) is the fact that you can choose your host. However their own hosting solution for $10/mo with a 250GB data cap is quite expensive. I can see that for smaller amounts of data Arq is more interesting, especially since it also stores history (which Backblaze does not).
It's worth noting that Arq can back up to Amazon Cloud Drive, which offers unlimited storage for $59.99 a year. As soon as they offered that I switched from Glacier storage; Cloud Driver is faster, cheaper and less fiddly.
However there is one last quirk I have with Arq + Hosting Service. If you need to retrieve your backup _fast_ you will have to reach for a paid service such as AWS Snowball which seems quite expensive. I can't to seem to find more recent information about them shipping smaller disks, just some old articles.