C. KDE/Qt/C++ programming is faster and more elegant. Again, this was a rather political decision. (Almost all GNU software is C-based, therefore GNOME has to be C-based, too)If you prefer C++, use GTK--. Also, are you aware that any KDE software you write **HAS** to be released under the GPL, unless you purchase a separate license from Trolltech and release as closed source? Qt is GPL, GTK is LGPL.
The LGPL is _far_ more flexible for a library license. That is a huge advantage for GNOME, in my opinion