Backblaze is actually rather bad at backing up everything that isn’t a file.
My other concern is that Backblaze doesn’t actually back up everything. It fails all but one of the Backup Bouncer tests, discarding file permissions, symlinks, Finder flags and locks, creation dates (despite claims), modification date (timezone-shifted), extended attributes (which include Finder tags and the “where from” URL), and Finder comments. Arq, CrashPlan (as of version 3), SuperDuper, and Time Machine all support all of these. Dropbox supports all of them except creation dates, locks, and symlinks.
Note that the post was originally written in 2014, but has been updated several times much more recently than that.
I have not done extensive testing, but if I had to guess, I would say that Arq is probably the best online backup for the Mac if you want a thorough backup that includes all the little details that you probably want and assume that Backblaze is backing up, but isn’t. Arq even has its own server/service now.
If you are using Backblaze (and I am, though only as a tertiary backup), you really should read the full article above.