Several years ago I had pretty good luck with the NXMachine server/client for a training system. I don't know if they still offer a free version or not :(
Yeah, NoMachine NX, used the free version ~2010, it was lightyears ahead of any other remoting solution for Linux. Presumably, the commercial product still is but there is no free version anymore.
There was a freenx project but it seems not much alive now. A different open-source project called x2go continues. The implementation seems less complete and stable but nevertheless, still a decent option for accessing a Linux desktop remotely over a lower-bandwidth (e.g. 3G mobile) connection.