is my suggestion to the table.
Small, clean, simple, fast, portable and free. Very good qualities in software I would say.
At the time (2 years ago) I tried several freeware backup/synchronization software pieces as I had to sync between a Windows XP PC (source) and a Linux file-server. Most of them would not even copy, some would copy partially. And then I found Pathsync.
Not only did it copy everything, it also did it fast. Not the copying in itself per se, but checking which files that were changed/added/deleted. It still amazes me. As it is only in version 0.35 and not actively developed anymore, there is a lot to be desired in the software. Still, as it is the software will fit perfectly with you.
All the other suggested tools are fine too.
It appears there is a new beta out since last month.