My wife and I held off upgrading last year because we are on T-Mobile and last year's iPhones did not include B71 600 MHz band.
Since 2018 models offer B71, we will be upgrading our 128 GB iPhone 7 Pluses.
It's unfortunate that iOS 12 did not bring Family Shared iCloud Photo Library. All of my family's 100,000+ photos and videos are on my iCloud account and thanks to iCloud Photo Library, my 128 GB iPhone 7 Plus has 80 GB free storage space.
So for me, 64 GB iPhone XS would be sufficient.
My wife will need 128 GB (hopefully iOS 13 will bring Family Shared iCloud Photo Library), and iPhone XR is the only one that offers this capacity ($799 USD). $200 premium for 256 GB on XS is harder to stomach. She rarely use the telephoto lens, so 128 GB iPhone XR for my wife.