The Beginner's Guide to Linux, Part 3: Choosing Your Window Manager and Desktop Environment
KDE4
The KDE4 desktop environment represents a significant departure from “traditional” user interfaces. To begin with, the desktop has been re-conceptualized as more than a place to store shortcut links. Although application shortcuts are still placed on the desktop, they are now limited to a small section. The rest of the space (that would otherwise be mostly wasted) may be used for small interactive widgets called plasmoids that provide additional functionality like post-it notes, resource monitors, RSS feeds, etc.

KDE4 is much more attractive than its predecessor, which looks rather dated in comparison. In terms of complexity, KDE 4.2 is essentially a compromise between GNOME and KDE 3.5. While 4.2 does not have quite as many features as its predecessor, it has slightly more than GNOME. Early in KDE4's development, many early users have criticized it for a lack of features (4.0 was a proof-of-concept release and was not ready to replace 3.5) but 4.2 has made significant improvements in this area and is adequate for production use. However, many KDE applications are still in the process of being ported to KDE 4 and may not quite fit the rest of the desktop environment in an aesthetic sense. However, this does nothing to adversely impact their usefulness.

Fortunately, the version of Dolphin included in KDE 4.2 is much better than the KDE 3.5 version. Many of the sorely needed features that the previous release was lacking have been added, and this goes a long way towards making Dolphin a viable replacement for Konqueror's file management functionality for most users.
KDE4 holds the middle ground between GNOME and KDE 3.5. If you prefer a healthy blend of features and simplicity, then KDE4 may be for you. In some distros, it is possible to install KDE 3.5 and KDE 4 side by side, so there is no reason to give up one for the other.
Fluxbox
Fluxbox is a simple window manager instead of a full desktop environment. However, Fluxbox is extremely lightweight and adds virtually no additional overhead to what you already have. As such, Fluxbox is best deployed on systems that have extremely limited resources or in instances where only a very lightweight window manager is preferred. Alternatively, Fluxbox is ideal for people who don't want any sort of user interface getting in their way at all when they work.
Unlike KDE and GNOME, Fluxbox acts more like some traditional Unix/Linux window managers from years past. There are no panels, icons, or anything else like that to click on; all interaction is done through the mouse. Right-clicking brings up the application menu, and middle-clicking brings up desktop settings. Fluxbox includes a bare-bones taskbar suitable for switching applications and desktops. Although it is extremely simple, Fluxbox still manages to be stylish with several different color themes to choose from.
If you enjoy truly minimalistic interfaces or can only allocate meager system resources to your window manager, Fluxbox may be perfect for you.
IceWM
IceWM has been popular on Debian-based systems in the past and has an appearance inspired heavily from classic versions of Windows. It is more intuitive than Fluxbox and has similar system requirements. During our tests, IceWM consistently started faster than Fluxbox did. While the IceWM interface is not going to win any beauty awards when compared to modern desktop environments, it is very neutral and won't get in the way when you're trying to work. IceWM also includes a CPU and Ethernet activity monitor on the taskbar as yet another testament to rugged usability.
IceWM is a good choice if you want your window manager to be simple and as close to Windows as possible while expending minimal system resources.