Depends on what you want to do. sshfs is great if you have internet; git is great. If you want to resolve stuff wrt both diverging; go for git. rsync also comes to mind; but I guess that can be a pain when merging.
Seeing dropbox is nothing more than sshfs + rsync, that would be a nice solution. I’d probably go with git myself, depending on the files being synced.
E: I saw someone mention encryption; encfs? SFTP is generally safe enough though.