XS & XS Max
Basically you're getting a gorgeous OLED screen, an extra camera for optical zoom, and a 4x4 MIMO for LTE. The rest of the phone is essentially identical to the XR. That isn't anything to sneer at since everything inside is improved over last year's X and the rest of the phones out there are still trying to catch up to Apple of 2017.
You get a great LCD screen but no haptic touch and just a 2x2 MIMO like in the past. You gain a neat new assortment of colors but don't most people put the phone in a case?
If you have a monthly lease (or the iPhone Upgrade program) then the cheapest XR will probably be the same or more than what you pay now. If you want the best get ready for your lease to cost more than your carrier's monthly charges. If you can afford to buy outright then prepare to feel like you are buying another laptop and not a phone.
Apparently Apple now thinks that no one wants a small phone. What happened to one-handed operation? Perhaps the idea is that with a connected Apple Watch and Air Pods and Siri we don't need one handed operation anymore. And no new small phone seems to mean no new cheap phone either. Maybe by next year these phones will migrate down into a price range that doesn't double the cost of cellular service.