Differences between the iPhone 5S and the iPhone 6 are a 4-inch screen on the iPhone 5s and a 4.7-inch screen for the iPhone 6, A7 dual core processor with an M7 co-processor for the iPhone 5s and an A8 dual core processor with an M8 co-processor for the iPhone 6. Both iPhones have an 8-megapixel camera and a 1.2-megapixel front-facing camera, but the iPhone 6 has digital image stabilization.
The iPhone 5s spots a 4-inch IPS LCD, while the iPhone 6 has 4.7inch Retina HD LCD screen with Ion strengthened glass. The iPhone 6 display is only slightly large than 720p, but the display has better color accuracy, the right amount of saturation and clarity. Both have the same 326 PPI pixel density.
They both are both 64 bit, dualcore, but the iPhone comes with an A8 processor, while the iPhone 5s has an A7 processor. Both iPhones have 1 GB of RAM but on the graphics side; the iPhone 6 has an upgraded PowerVR GX450 CPU, while the iPhone 5S has a PowerVR G6430.
On the camera side, an iPhone 5s has an 8-megapixel sensor, 1080p HD video recording, TrueTone flash with a 1.2-megapixel front-facing camera, while the iPhone 6 comes with an 8-megapixel sensor, TrueTone flash, face detection, a 1.2-megapixel front-facing camera, 1080p HD video recording with digital optical image stabilization. The upgrades on the iPhone 6 camera provides better low light shots and more image detail compared to the iPhone 5s.