Use the tarballs. You can use the rpms if you would rather, but I heard that tarballs are better for source because they provide more flexibility.I have noticed you doing alot of compiling of KDE -- how much am I in for if I decide to compile it myself? *Source tarball or .src.rpm -- I dont care personally, I just want to steal some speed and am thinking about compiling.
Either way, compiling KDE and QT is a long process depending on how much you want to compile (I believe there are only four libraries that must be compiled to have a working KDE install and a dozen more add on libraries that can be compiled and installed later on). You can still use your computer (depending on how fast it is) while you compile in the background. That is what I did. I compiled most of KDE 3 while running KDE 3. Then I exited for a few minutes as I ran make install and restarted with all of the new features and programs I just compiled.
I even wrote a script to download and compile every library from the CVS tree, but the CVS tree kept blocking me from accessing their server for several minutes at a time, but it was enough to stop the script in itís tracks.