At a glance:

SpiderOak offers encrypted backups. This is a good thing. It doesn't specify how it's stored on their end (presumably because it doesn't matter to the end user). So that's an unknown.

Bytejail offers encrypted anonymous backups (via Tor Hidden Service) and uses a TahoeLAFS backend. My understanding of TahoeLAFS is that it's excellent. So if you're security-conscious, Bytejail would seem like a better choice.

(I'm not familiar enough with SpiderOak to comment on their offering in detail; I can only really go off the page you linked.)