This was a shootout between four phones, but the real question is whether the Samsung Galaxy S6 has improved over its 2014 predecessors. A full year divides the Galaxy S5 and S6 and between them there was distinct improvement.
The Galaxy Note 4 is more recent and benefits from some of the same camera improvements that the S6 boasts, most notably, the Sony IMX240 sensor and the optical image stabilization.
Galaxy S6's contribution to the camera department is a wider aperture f/1.9 and the newly added Pro mode. We haven't really seen apertures this wide on a smartphone (save for the Nokia Lumia 735, and that was a 6.7MP camera), so it was interesting to see it perform in the dark. The combination with OIS seems to be a winning one - it can keep ISO low with slower shutter speeds, but not too slow.
Both still photos and videos capture more detail and less noise compared to the Galaxy S5 in the dark. The difference gets bigger with the fading of the light - the S6 took usable shots where the S5 smudged the whole image. The new model tops the Galaxy Note 4 as well, though the difference here is slimmer.
Recently Samsung has been changing its tune - the bloated TouchWiz got trimmed, the aging hardware design was revamped and the camera software known for oversaturation and oversharpening has now done a 180° too.
Daylight photos appear softer than the Galaxy Note 4, but that's largely because the Galaxy S6 applies almost no sharpening. This (and the generally improved camera) keep the noise to a minimum, the images look less processed and less like a typical phone camera shot.
As we concluded, there were some issues with color processing in the red channel, but that was more of an edge case than a consistent problem.
The Apple iPhone 6 is a new device though its basic camera hardware has gotten only incremental improvements since the iPhone 4S. It held its own at 1080p video (both at day and at night), panorama too, but the 8MP sensor is holding back the camera.
The Samsung Galaxy S6 camera is a definite upgrade over the Galaxy S5 - especially in the dark, but visible in the daylight too. As for Galaxy Note 4 users, there's no reason to toss out your beloved phablet yet but this is a great preview of what's coming with the Note 5.