Once the new iPhone 11/XI is released the prices of a good used X or XS will drop as people upgrade and a lot hit the market. I have no experience of the XR but it has an LCD screen and older camera; whether it's much of a difference in the real World I can't comment. If buying used ensure you ask what the Battery Health figure is; anything under about 85% indicates a tired battery so factor in a replacement - £45 I believe through an Apple Store.