Even after sunset, the Microsoft Lumia 950 XL managed to underexpose its photos, it really did not make good use of its dynamic range. Below is the histogram for the low-light photos we took.
You can see how the histogram hugs the left edge (those are the underexposed shadows) and how empty it is on the right (showing limited dynamic range after processing). Colors are off, noise is visible and resolved detail is about on the same level as the iPhone 6s Plus.
Now, the Lumia 950 XL shot at a fast 1/21s shutter speed, which will keep motion blur relatively low, while the iPhone 6s Plus used a glacial 1/4s shutter speed, overconfident in its OIS. Still, looking at moving cars shows even the Lumia isn't blur-free.
The iPhone did a good job on this test, despite having the narrowest aperture (f/2.2) and lowest resolution (12MP). Sure, the shutter speed is very slow, but it kept ISO low so there's less noise in the photo.
The LG V10 leaves more noise in the shot, but photos are sharper by quite a margin. The 1/11s shutter speed is slow, but the OIS is there to help with hand-shake blur.
The Galaxy Note5 trades some of the sharpness to remove much of the noise. This effect is stronger in some areas, creating patches of low detail.
Winner: Samsung Galaxy Note5. It resolved more than the iPhone in some areas (but less in others, it was inconsistent) and didn't mess up the dynamic range and colors like the Lumia.
Runner-up: Apple iPhone 6s Plus. With night shots, noise becomes the limiting factor rather than resolution. The iPhone handled it well and it was a hard call between it and the Note5.
Third place: Microsoft Lumia 950 XL. Poor processing buries a lot of detail in the pitch black shadows, noise complicates the issue further.
2160p video camera
The Microsoft Lumia 950 XL captured a lot of detail in its 2160p video and kept the noise low (with some color noise visible), but it again botches the colors.
Even the impressive LG V10 lost some detail to noise, putting it behind the Lumia on that metric (the noise gets very noticeable in places). Still, colors are visible even without pixel peeping and should have been a priority.
The Samsung Galaxy Note5 smooths out its image, which minimizes the visual snow effect you see in noisy videos, but it kills a lot of the detail.
The Apple iPhone 6s Plus had a hard time in the dark, its videos came out quite dark and with a lot of noise. The resolved detail is still less than the Note5, without the benefit of reduced noise.
Winner: Microsoft Lumia 950 XL. The video came out surprisingly crisp with moderate amounts of noise. The colors are way off the mark though.
Runner-up: Samsung Galaxy Note5. Noticeably less detail, but from a distance (e.g. watching a large TV from the couch) the noise may become more noticeable than the lost detail.
Third place: Apple iPhone 6s Plus. The videos are just too dark and noisy.
1080p video camera
The lower resolution discards some of the detail resolved by the Lumia 950 XL, so shooting in 2160p is actually beneficial even in the dark. Colors remain problematic.
The LG V10 picks itself up, the lower resolution helps it cut down the noise and the narrower field of view makes it easier to produce a more detailed image. For the V10 we'd go the opposite way of the Lumia - shoot 1080p in the dark (if you can fit the scene in the tight FoV).
The Samsung Galaxy Note5 gets a boost too, but not quite enough to catch up to the Lumia.
Note that we shot the 1080p samples last and the sky had gotten noticeably darker than it was for the 2160p shots. The other three managed it fairly well, but the iPhone 6s Plus shot a very dark video. You have to boost the exposure manually when shooting with the iPhone, otherwise the results will be unusable.
Winner: Microsoft Lumia 950 XL. It lost much of its lead as the lower resolution puts an upper limit of what can be done.
Runner-up: Samsung Galaxy Note5. A fraction behind the Lumia in detail, but with better colors.
Third place: Apple iPhone 6s Plus. Increase the exposure manually (and accept the extra noise) or you won't see much in the videos.