Kubuntu is one of the distros which didn't undergo a lot of change over the last 2-3 years. Mostly it has been a stable distro with a stock KDE interface and a mix of KDE-nonKDE packages. Though it may not be called the best KDE distro around but it is definitely popular. Unlike distros like OpenSUSE or Chakra, Kubuntu never came with any distro-specific themes but relied more on the stock KDE