Once light levels drop, things get tougher - talk about stating the obvious. Shooting at dusk, we noticed the iPhone routinely exposed darker - to the tune of a half to a full stop difference. This, rather obviously, leads to a two-fold set of consequences - it better preserves point sources of light from blowing out, but does leave shadow areas too dark.
Looking up close, we can see that the iPhone has a minor advantage in resolved detail, but only where there's enough light. Noise levels are comparably low with both phones.
The iPhone's already more muted colors appear further desaturated at night, while the Galaxy hasn't lost a bit of its pop.
Shooting with the telephoto cameras at night is best avoided - smaller sensors and individual pixels and a narrow aperture don't mean great light gathering capability. Fully aware of that (dare we say, even better than us), the engineers at both companies resort to a cropped and upscaled image from the main cam when you hit the '2x' button in low light.
The threshold is apparently slightly different between the two as the 'Sofia ring' shot is actually taken with the telephoto camera on the iPhone, but the standard one on the Galaxy (and both are bad in their own ways.
Anyway, general low light samples with the phones zoomed in to '2x' aren't really something you want to to be examining at 1:1 magnification.
Now, there's a loophole that was left in both makers' camera apps that effectively does let you use the telephoto cameras in the dark and it's called portrait mode (okay, technically Samsung calls it Live focus). Since both portrait modes use the long lens module, you can be certain the phone won't default to the main cam - with no 'portrait' subject in sight for the algorithms to isolate you'll just get a zoomed in photo in the dark.
We experimented briefly, shooting the same scene in the respective auto and portrait modes and it's plenty obvious why you wouldn't want to use the Galaxy's telephoto camera in low light - the cumulative effects of the limiting hardware and the noise reduction result in a pretty bad image. Meanwhile, the main camera's digitally zoomed-in shot is much cleaner, and in fact more detailed.
The difference isn't as striking between the iPhone shots though. For one, its telephoto camera produces a significantly better image than the Galaxy's telephoto. And then the one taken on the main camera is very much alike.
Speaking of portrait modes, let's use them the way they were intended instead. Apple's way of doing things has been to isolate an oval outlining the face and keep that in focus and then gradually start blurring towards the periphery so it doesn't have to bother with detecting the precise border where subject and background meet. That generally works slightly better with humans than the Galaxy's way, particularly with pointy hairstyles, though with less demanding outlines the Note9 is as good.
What the iPhone does do better is dynamic range and skin tones. Faces are well exposed, with no blown out spots, and colors are very... human. The Galaxy's portraits, while okay, don't quite have the same natural look to the skin tones, and also exhibit a tendency towards overexposure of the faces.
Apple's also got the upper hand in rendering point lights in the backgrounds - who doesn't like some nice bokeh balls? The iPhone image is a lot more convincing and the circles of light look much more pleasing compared to the Galaxy's general mush of a background. Sure, you'd need to get the proportions of the the subjects and lights right as well as the distances between them and the phone, but with a little trial and error you're in for some nice bokeh. We're also providing a photo from a DSLR for comparison purposes.
Looking at the specs, you'd think that the Galaxy should have a vastly superior selfie game, but in reality, that's not necessarily the case. One area where it easily wins is coverage - we still feel like its 25mm equivalent lens is better for selfies than the iPhone's longer 32mm equivalent, at least until there are two different focal lengths on the same phone to choose from (wonder if someone's done that). The upside to Apple's lens choice is that generally speaking, a 25mm lens like the one Samsung is using is much too wide for a flattering perspective of a face.
Once again, the iPhone's skin tones are arguably more pleasing, with an extra bit of warmth that is missing on the Galaxy. The Galaxy leans towards a pinkish skin rendition, while the iPhone is a bit yellower.
And yes, Apple's Smart HDR ensures that face gets the right exposure and does a great job of avoiding blown out highlights.
The iPhone's disadvantage-turned-advantage with its longer selfie lens can be observed in selfie portrait shots (or Selfie focus in Samsung speak). The focal length, combined with whatever magic takes place with the TrueDepth camera means the iPhone takes the better portrait selfies as well.