SuperSaf did a nice camera comparison between the S10+ and the XS Max today. You can check out the video and judge for yourself:
I personally find the colors to be a little better on the iPhone, while the overall contrast seems to be better and more punchy on the Galaxy (at least with the rear cameras). The steady-shot stabilization on the S10+ is absolutely incredible and delivered a really stable and near-motion-free video even while he was running (the feature can only be utilized at 1080p recording though). Both cameras were very good at the portrait mode stuff, with each suffering from just a couple of hiccups here and there, but the AI stuff should continue to improve the algorithms going forward.
Samsung continues to provide superior low-light performance on their cameras with the dual-aperture setup they released last year on the S9. It really is quite amazing how good the shots are, despite being taken in near pitch black conditions. Interestingly, the front-facing dual-cameras on the S10+ didn't provide a superior performance to the iPhone's single lens setup IMO which is a shame. I really wish Samsung had used the same single-lens setup on the Plus as they did with the regular S10 as it really doesn't seem to add anything while also making the hole-punch in the screen twice as large as it needs to be. I personally wouldn't even care if my phone didn't have a front-facing camera, but I know I am in the vast minority on that one.
Overall it looks like the S10's have a very competitive lineup of cameras with a ton of features and configurations that compare very well to the iPhone XS Max anyway. Will be interesting to see more in-depth camera tests between the S10+ and other phones like the Pixel 3XL...