Overall these two models are extremely similar. The iPhone 6s and iPhone 6s Plus are both offered in the same storage capacities of 16GB, 64GB and 128GB, the same colors (gold, silver, space grey and rose gold) and they both have almost the exact same functionality. With multi touch retina HD displays and LED backlit screens, these iPhone still offer a good visual experience.
The main difference comes down to the size of the handset and the battery life. The 6s Plus has a 5.5 inch display with a battery to support approximately 12 hours of internet browsing. Whereas the 6s has a 4.7 inch display with about 10 hours of internet browsing time.