There's a number of upgrades from the iPhone 6 in the iPhone 6S. Some include a better camera with higher resolution (8MP to 12MP). Also the 3d touch that let's you now bring up context sensitive menus and a bunch of other functions by how hard you press the screen. There's also a faster processor in the iPhone 6S with the A9 vs. the A8 in the older model. There's also software upgrades and improved SIRI integration...but to be honest the older iPhone 6 will get these upgrades to when the OS is updated to iOS 9. Finally only the iPhone 6S and 6S Plus come in the new 'Rose Gold' color so if that's a 'must have' you have to go for the newer phones.