RDP has better throughput than VNC, yes; but the RDP framerate in the official Microsoft clients leaves a lot to be desired. The open-source rdesktop client uses a much higher frame-rate that makes the experience seem more fluid, whereas mtsc.exe is artificially
hardcoded to something like 20fps. For this reason, in LANs at least, VNC gives a better zero-configuration experience.
Frankly, I have NEVER seen even ONCE that VNC would work better than RDP and I have used both in all kinds of scenarios.