If You're going to use a GUI, use KDE4.

Well, if you are going to use a GUI, use KDE. I like KDE because of the freedom it offers, meaning it is the most flexibility, customizable and feature rich window manager out there.

Here is my assessment of some of the most familiar window managers in Linux.

KDE
Pros: Tons of options so you can customize the heck out it. Looks good. Easy to use.
Cons: Bloated. Too many options (for those who don't like choice).

Gnome
Pros: Easy to use. Looks good. Moderate customization, but not overloaded like KDE.
Cons: Moderate customization. Bloated.

Xfce
Pros: Light on resources. Gnome looking. Pretty. Easy to use.
Cons: Gnome looking. Minimal customization.

Fluxbox/Openbox/Blackbox/FVWM
Pros: Very light on resources. Highly customizable. Minimalistic.
Cons: Takes forever to customize and most customization is done by editing config files.

WMaker
Pros: Light. Unique environment.
Cons: Very few customizations.

JWM/IceWM
Pros: Light. Easy to use.
Cons: Windows 9X feel and look. Few customization options.

Enlightment
Pros: Light. Very unique environment.
Cons: Very unique environment. Takes some getting use to.

There are others out there as well, but this list covers about 98% of all the Window Managers used in Linux. You should notice that many of the Pros I listed are also Cons. I did this on purpose to demonstrate that it's really a matter of preference. One is not really better then other, it's just a matter of what fits you the best. I've tried each of these and I like KDE the best, but on some of my older machines where KDE is too slow, I use Flubox or Openbox. I tend to lean more on Window Manages with a lot of customization.

If you haven't tried some these window managers give them a try. You may be surprised and find a new favorite window manager.