I have a sit/stand desk so mine's on top, it makes organising the cables much easier.
Nothing as swish looking as a Mac Pro though, it's a plain black Lian Li behemoth from the late 00s.
I also have a standing desk, and my desktop computer is still on the floor. That way I can just route all the cables to the back and then under the desk to my PC. Looks very clean as well.
I also have a standing desk, and my desktop computer is still on the floor. That way I can just route all the cables to the back and then under the desk to my PC. Looks very clean as well.