Kevin Carter z DxOMark:
From our industry-standard series of tests both in the lab and real world use, the iPhone 6 and 6 Plus perform very similarly. They have very good, generally reliable auto-exposure in a wide range of lighting conditions and they have both fast and accurate autofocus. Output from the 8-Mpix stills improves the high level of detail in both outdoor and indoor lighting. In low light, noise reduction is handled well with images revealing fine-grained luminance noise and little of the distracting color (chroma) noise.
The main differences between the 2 cameras come from the OIS present in the iPhone 6 Plus. On one hand, the OIS helps to increase still images exposure time in low light, leading to better noise performance. Ghosting on HDR images also seems smaller with the iPhone 6 Plus, probably helped by the OIS that ensure a good registration between images. On the other hand, we have observed a video stabilization artifact, on the iPhone 6 Plus, most likely linked to the OIS control that lead to a video stabilization score slightly lower for the iPhone 6 Plus than for the iPhone 6.