xfce4 is a good choice for Debian it is lightweight and easy to use. KDE4 is probably the best desktop on Linux right now, but it's too resource hungry to be the default Debian environment, imho.
""KDE4 is probably the best desktop on Linux right now"
I strongly dissagree."
I strongly disagree with you. KDE is not perfect but at least gives freedom to customize it a lot, and without need to swing in config files.
I remember when I tried GNOME 3 in Debian wheezy. I could not work out how to do anything at all. Literally, the only button to click on was the one to exit. So I did.
And I remember the first time I used GNOME 3, it was a great experience, I pressed the Windows key and a few letters and I could launch the program I wanted, I could press the winkey again and have an overview of my openned Windows, I could press ctrl+shif+arrow up or down and I could switch from one virtual desktop to another, I could press alt + the key above tab and I could switch betwen the Windows of the same applications, there was barely the need to use the mouse or navigate in menus to click something, It was an awesome, intuitive and productive experience, cause the desktop was getting out of my way, that was my first experience with GNOME 3.