They are both much, much faster than X11. X11 has higher latency and uses significantly more bandwidth.
In my experience, this hasn't been the case. Running Emacs via X full screened across two monitors (both at 1920x1080) is much snappier than running VNC from a Windows box, single screened, lower resolution (can't remember exact numbers just now) and lower BPP. Of course, that could just be the typical disparity in IO performance between Windows and Linux.
And while I grant that X sessions can't be detached by default, there are solutions for that (see XPra further up thread). There's also been compression for X quite some time. On top of all of this, you don't even have to be running an actual GUI on the serving end; can the same be said for RDP and VNC? Or Wayland?
In my experience, this hasn't been the case. Running Emacs via X full screened across two monitors (both at 1920x1080) is much snappier than running VNC from a Windows box, single screened, lower resolution (can't remember exact numbers just now) and lower BPP. Of course, that could just be the typical disparity in IO performance between Windows and Linux.
And while I grant that X sessions can't be detached by default, there are solutions for that (see XPra further up thread). There's also been compression for X quite some time. On top of all of this, you don't even have to be running an actual GUI on the serving end; can the same be said for RDP and VNC? Or Wayland?