KDE Plasma 5.x series is widely accepted for it's appearance and performance. KDE Community just revealed a development version of Plasma 5.4 which includes a brand new launcher.
According to a news article published in softpedia:
Plasma 5.4 has been revealed by the KDE Community, and the developers have made a series of very important changes and improvements that will soon land in the stable branch of the desktop.The KDE Plasma desktop has seen some pretty amazing modifications in the past few months, and developers have continued to push for even more improvements. Each new edition of Plasma has been a great success, and it looks like there is still room for improvement. If we keep in mind that Plasma is basically the first thing a KDE users sees, then it's easy to understand why any upgrade to it will be noticeable.