Generally, I do fresh installs. Even at my old job, where Fedora was my main workstation, I would pop in a new drive, install the latest Fedora, then copy over.
Today, taking out a laptop I haven't used in awhile, I decided, since it didn't really matter if it broke, to try dnf system upgrade from 23 to 24. I have rpmfusion on this. It was made from a minimal install, then adding X (using dwm compiled from source).
The upgrade went completely smoothly. I followed the instructions on https://fedoraproject.org/wiki/DNF_system_upgrade
and it all went as I wanted it.
Note there was nothing really odd about this machine, save perhaps, for the fact that dwm is compiled from source. Still, it was a pleasant surprise, and easier than doing a fresh install.