As a user of noVNC, I'd be interested in such comparison, too. I haven't used Guacamole, but as I understand, sansnomme's point is that Guacamole compared to noVNC is like Visual Studio compared to GCC - while GCC and noVNC offer you most basic tool, Guacamole and Visual Studio provide some helper utilities around - like session management, config UI, etc.

So when compiling single-file "hello world" app or connecting to a single machine you would prefer a simpler tool (GCC/noVNC), since more complex tools require more complex workflow; but for more complex projects (or when you have tens of machines under your control) you would prefer more complex tools.

Disclaimer: I have never used Guacamole, used Visual Studio very little, and my experience with GCC is rather limited.