TouchWiz has been rebuilt and improved on the Galaxy S6. Its over-cluttered design has been cleaned up – and it's about time. It is now simpler, has fewer menu options and less scrolling is needed. The Galaxy S6 shipped with Android 5.0.2 Lollipop. In comparison. Apple’s iPhone 6 comes with the latest iOS, which is iOS 8.
For obvious reasons, both with regards to space limitations and difficulty of comparing Apple software and Android software, we will not bother to try to tell you which operating system is better. You will know which one you prefer and how big a difference there is between them and we know there's not much we could say to make you change your mind.
In the spirit of fairness, we do find the iOS system to be very stable and smooth, with basically no software glitches to speak of. The same can be said of TouchWiz, which has been completely overhauled since previous versions and is now as fast as it has ever been and almost as stable as iOS. To be sure, TouchWiz has more features, customization options and settings than the iPhone 6, but whether that is important to you is a matter of personal taste.