In my opinion, the above three IDEs all have their strengths and weaknesses depending on what kind of project you are working on. Here are some of my observations.
KDevelop is probably the most comprehensive IDE of the three. This should not come as a surprise as it has been around for more than 10 years and it bas been the de facto development environment for most of the KDE development work. It is very feature rich and you can use it to develop many different types of applications natively out of box (e.g. KDE, GTK+, Qt, wxWidgets, etc). If you are developing GNU style applications, you will benefit from the Automake project type if provides. Besides the vast functionalities KDevelop provides, it is also very fast, efficient and stable.
Nonetheless, KDevelop is not the most intuitive IDE and does not suit small projects (e.g. prof of concept code) well as the initial project setup can be time consuming.
Code::Blocks is a very capable IDE for C++ development as well. It offers many project templates even though it does not offer native KDE project types. This should not be a problem to most people however. Among the features I like the most is that it does not require explicit make file configuration and the build dependencies are inferred by default. This makes it very attractive for rapid prototyping. Debugging under Code::Blocks is also a pleasant experience. It also integrates (at least in the later SVN versions) Valgrind‘s MemCheck and Cachegrind, which are very useful for detecting memory leaks and tweaking algorithms for the maximum performance.
The latest stable version of Code::Blocks is 8.02, it is a little dated as a lot of functionalities have been added in the later SVN builds. If you do not require the most stability (I have run into some issues recently), using SVN build should not be a problem. The editor (e.g. syntax highlighting, collapsible regions) is a little bit buggy though and the contextual help does not always work to the level of detail I desired.
NetBeans C++ IDE is probably the most beautiful one among the three. It offers the most detailed syntax highlighting, and can be configured to display class hierarchy and library function information. The refactor tool works pretty well and is certainly a boon to large scale development. Its contextual help is also of top-notch.
All of these come at a cost of course. NetBeans C++ IDE is the most resource intensive among the three. It can easily use 500 MB memory when doing development and can be sluggish at times. It also comes with a very limited project template (e.g. no out-of-box project templates for Qt, wxWidgets). Certain settings are hard to get at as well. Nevertheless, if I am primarily writing back-end code, NetBeans C++ IDE could easily earn my top choice.
Some people like Anjuta and compare it favorably to Code::Blocks. But I haven’t got a chance to use it yet.