Which one of the IDE is good in terms of support for debugging, implementation and usabality. Qt or KDevelop?
Various duplicated:
http://stackoverflow.com/questions/86676/is-there-a-good-and-free-ide-for-cc-in-linux
http://stackoverflow.com/questions/211924/best-development-ide-for-linux-closed
Some of which have already been closed.
You seemed to be confused. Qt is a C++ toolkit. KDevelop is an IDE.
From your comment I see that you meant Qt Designer. Designer is not an IDE; it is just an application for graphically creating user interfaces. It can't compile code, debug, or do any of the other things an IDE does.
The KDevelop IDE actually embeds Designer into itself, so this clearly isn't a "one or the other" type situation.
Of course a third possibility is that you were talking about Qt Creator, the IDE that was recently released as beta by Qt Software. If that's the case, then I would just encourage you to try them both out and see which you prefer. They take different approaches and the better option would be based almost entirely on personal preference.
I think that you mean KDE with KDevelop, it depends on the scope of your application if it will be desktop independent I will go to Qt, if you want to make an application that uses all KDE power I will go KDE.
For Windows and embedded developing go to Qt.
The opening post probably meant Qt Creator, which definitely is a complete IDE.
Qt creator comes in two flavours: a simple one which is Open Source and is licensed only to create Open Source software, and a paying one which is licensed to create both OSS and closed-source projects. Qt Creator is just as portable between platforms as Qt itself and uses the MingW compiler under MS Windows and the GCC compiler under Linux.
Generally speaking I found Open Source Qt a polished piece of software which gives a much smoother and more pleasant user experience than KDevelop (which tries so desperately to implement slews and slews of bells and whistles that it neglects to make simple things easy and reliable), and it has few features and a much simpler interface than Kdevelop (perhaps the paying version also has a more complicated interface).
Using the Qt framework exclusively allows you to easily make applications that run under Linux and MS Windows with no more than a recompile, and which look the same on both platforms. KDE on the other hand is Linux-only.
What I especially liked is that importing about 35 files from a commandline app (originally developed under MSVC), having qmake set up the makefile and then compiling it worked like a charm, as opposed to KDevelop where it's a big hassle. It's easy to have Qt Creator set up a commandline app too. Now that the commandline version compiles I can easily make a Qt GUI to prepare the options arguments, set the parameters, pick and click all the input files, and set the output directory. The only thing I have to change is to change my previous "main" function into something else, let Qt generate a main app for me, and then and call it in response to a buttonpress. I had such a hell of a time trying that with KDE and Kdevelop a year or so ago that I completely gave up and went back to MSVC.
Unless you really really want to develop for KDE only and are determined to use KDE functionality that goes above and beyond Qt, I would choose Qt Creator.