[ale] Best, Secure, Fast Remote Desktop?

[JD]

Every year or so, I look for a better way to handle remote desktops for the 2%
of the time I need one.  ssh works the other 98% of the time.

For the last 3+ yrs, FreeNX + remote NoMachine v3.5.x client (Linux/Windows) has
been working extremely well. I'm using it now. I understand that FreeNX isn't
working on Ubuntu 14.04 (yet?),

Requirements:
* Linux-based remote desktops (don't want Windows)
* secure (key based); MANDATORY
* stable; MANDATORY
* fast performance for "productivity apps"; MANDATORY
* Clients must support Windows and Linux, Android is nice-to-have
* install from well-known repos, PPAs - NOT SOURCE
* F/LOSS
* don't need video streaming and
* audio is nice-to-have

Has anyone switched over to x2go since FreeNX seems abandoned?
http://askubuntu.com/questions/466309/freenx-server-installation-on-ubuntu-14-04-trusty

If so, how is the performance, usability, stability of x2go?
Is the performance similar to NX or better?

Has anyone setup a Guacamole server? This is a HTML5, web-based remote desktop.
I'm less thrilled about allowing the entire world access to the front-door of a
network. Would only deploy this with a VPN mandatory. Still - any users out there?

Respect to RDP and VNC users, but compared to NX performance - those are dogs
and both require a separate tunnel/vpn for security. I actually remote into NX,
then connect to Windows machines with RDP on the same LAN. Works good enough.