Satoshi Nakamoto always referred to it as such:
block chain
However, I see the term "blockchain" used a lot anyways. Do you think we should use Satoshi's terminology to prevent confusion with Blockchain.info, who will usually just refer to themselves as Blockchain? Or am I worried about nothing?

Pretty interesting find that Satoshi used an space between block and chain. Personally I say blockchain because im used to blockchain.info, or Blockchain if it's the begining of a sentence lol.