I am pushing from dropbox to origin master, in general, just so that the GitHub repo is updated slightly faster than when might push my local master changes. I don’t think it really matters either way.
I like the idea of a dropbox branch always automatically reflecting the state of the Dropbox folder, and one might be able to do this with some webhook approach that doesn’t require a server. The Dropbox API also lets you get version history, so one could use that to make a bunch of auto-commits to a dropbox branch that reflect the changes.
I’ll see about a diagram in a bit.