Here are my biggest problems:
* On X11, after waking from sleep, fonts are sometimes garbled. This is easily fixed by restarting GNOME. I never have to do this with Wayland.
* On X11, I always have to manually rearrange my monitors every time I plug them in, because some part of the stack doesn't know how to remember them. They work perfectly on Wayland.
* On Wayland, GNOME's Night Light feature does not work. Night Light tints things red in the evening to help me sleep.
* On Wayland, some apps misbehave in strange ways. Electron-based apps are sometimes slow to react to input, but updates have been fixing this. Also, Calibre's Ebook Viewer perpetually hangs. I have no idea why.
Fortunately, switching between X11 and Wayland is pretty easy--just a log out and then back in after specifying which one I want.
Gaming is different. It rarely works on Wayland. Much better on X11. But I don't game very much, so this is not based on a really wide selection.