Should I install the version in my apt repo (6), or (7) or (8)?

Also, I'd like to know what the major difference is in the versions, I've googled this and found nothing.

(other than bug fixes and "repo format changes"), I wanted to know if the repo format change is a good reason to try to run the latest v8.

edit: I guess there is no "release notes" link for git annex? I see the content that would exist there in news: