I myself prefer a fresh install on each release, though I tend to skip every second release.
Rather that install over the old system, I typically install into a partition separate from the old one, so both old and new systems are bootable, and accessible from each other, for a period of time. Home and data partition are separate to root.
The last time I did this I did not use a bootable disk (USB) to install, but use the DNF running on the old system to install the new system onto the new partition! Quite an experience, some quirks, but it worked!
The attached text file is the steps I took (for fedora 24)