Black levels are one attribute of a screen. However the Xr also has a few upsides: A higher brightness, and no display flickering due to PWM. I personally thought the Xr also exposed less yellow screen tint than the Xs and scrolled with less blur and distortion, but that might have been subjective.

The other thing that is often advertised as pro for the Xs is a higher resolution. However that is not entirely true, since the Oled displays use a pentile matrix, where there is not a full sub-pixel available for each pixel. Which means in other words the difference in actual resolution is not as high as the pure numbers might want one make to believe.

I think both displays are excellent, and won't disappoint.

I did not expect OLED to be this much better than LCD before I got the X. It makes an absolutely enormous difference when you use the phone in a dark environment, say to check the time if you wake up at night.