RDP is so much more better and advanced... and faster and 1000 other things that I'm afraid VNC doesn't come close to it. I would NEVER work via a VNC client but working with RDP is a pleasure.
But yeah, that web thingy won't run on these "thin" clients so :/
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.