Best will be different for different people, but I find the sort of ad-hoc networking you want to do is best done with ssh and fuse. It's not just for file transfers either. You can run applications remotely and use the remote system as a proxy server. Rsync works well over ssh, and of course just using it to log in as a terminal is handy too. It can be as secure as you want it to be, and can even do port forwarding. Once you know how to use ssh, operating systems which don't have it available natively just seem inadequate.
For your intended use, make sure ssh-server is installed on the system you want to connect to and fuse and sshfs are installed locally, then use sshfs to connect to that server and mount the drive somewhere in your local file system. I would use something like: