The iPhone XS Max has the best display in the history of best displays. I don't mean that to sound blasé or sarcastic. Apple's teams, from silicon to industrial design to display technologies did a tremendous job on it.
There's just something hinky about how these shootouts appear, and switch between Apple and Samsung, every quarter. It's why I've always preferred AnandTech's display tests. Sadly, though, they don't seem to get those out regularly, if at all, any more.
Apple has continued to raise the on-screen Absolute Picture Quality and Absolute Color Accuracy of their displays by implementing Precision Factory Display Calibration, moving the overall iPhone XS Max display performance up to Record Setting Outstanding levels, and setting many new Display Performance Records, including Absolute Color Accuracy at a very impressive 0.8 JNCD that is Visually Indistinguishable From Perfect, and almost certainly considerably better than your existing Smartphone, 4K UHD TV, Tablet, Laptop and computer monitor. The iPhone XS Max also has a Record High Full Screen Brightness for OLED Smartphones of 660 nits, considerably brighter than most OLED and LCD Smartphones.
Compared to the original iPhone X, the iPhone XS Max has notable improvements including higher Full Screen Brightness and higher Absolute Color Accuracy, all the more impressive because its display is 22% larger in Screen Area, which is more challenging to manufacture.
Subjectively, iPhone XS and iPhone XS Max have unbelievably good looking and, to my eye, color accurate displays. Objectively, I wish there were many more places that performed rigorous display testing.
Either way, DisplayMate's is worth a glance.