A lot of this is really personal preference and how you'll be using the phone.
While working, I always got the latest, greatest phone every two years to get "the best" features, which were often used. Now that I'm a bum, I've been on the Samsung S5 since I bought it when it first released.
I'm not sure any new phones do too much more in areas like onboard cameras, at least to the point where it's really user noticeable. Latest phones will be faster, but will they be noticeably faster to the user? Depends on what you're doing with the phone.
The one area, where even with my reduced usage, that I would consider an older generation phone a negative, is onboard memory. I only have 16GB, which would have been plenty three years ago, but with apps getting bloated and with just collecting apps over time (many of which won't go to the SD card) I wish I had 32GB or more. At this point, I'm always, after app updates, having to move apps back to the SD card (because some apps reinstall themselves onboard after updates) and I also keep some apps in my cloud library that I would rather have installed on the phone.
So after all that writing, I would just suggest getting the most device (vs SD) storage that you can get.