The perfect desktop would be the one you design yourself. Failing that, which of the main Linux desktops is right for you?

A few months ago, this question came to a choice between GNOME and KDE. Now, with the introduction of GNOME 3 and Ubuntu's Unity, the question has become more complex.

Should you accept the latest innovation, or go with a desktop that proves itself? A simple desktop, or a complex one with all sorts of customization? One that doesn't change, regardless of whether you are using a mobile device or a workstation, or one that changes to fit the limitations or advantages of each computing device?