What iPhone should I get?

My recommendation (based on the choices you included) is to buy a new model and get either the XR or the SE. This way you will future-proof your phone for longer. Then, it boils down to whether you want a larger screen or a smaller screen and whether you want Face ID or Touch ID. The XR is larger, is all screen and has Face ID (no home button). The SE is smaller, has bezels, and has Touch ID (with a home button). I have had an XR for two years and it is a great phone.

The one that best meets your needs and budget. Use the comparison tool to compare the different models:

iPhone - Compare Models - Apple

Go on the Apple site, compare the phones, then choose the one that best meets your needs. If cost is a concern, then look at the se 2020.