Both are pretty great on Fedora, although Fedora gives Gnome just a tiny bit more attention, and even specifically align Fedora’s release schedule with Gnome’s.
Gnome will likely be a bit more stable, consistent in UX, and have a workflow that’s very different but pretty amazing when it “clicks”. Gnome has a pretty great Adwaita app ecosystem that matches the system theme very well. Features can take a little while to come to Gnome, because the devs are pretty anal about getting things implemented perfectly before they’re added.
Plasma is more powerful and customisable, most parts of the system, and apps in the KDE app ecosystem, have a load of options you could spend hours going through and customising to your heart’s content. Plasma out of the box pretty much operates like you’d expect a Windows PC to work (sans the enshittification of course lol) . Plasma adds features rapidly, and just works out the kinks while in production, so-to-speak.
Both of them are great, albeit very different, which keeps the Linux desktop interesting and varied IMO. I’d try both for a day or two and then make your choice, because it’s highly subjective.