If say this depends on what your GUI experience and tastes are.
The one I've been keeping my eye on but haven't had a chance to use yet is Tauri which wraps the system-provided webview nicely, so you can treat it like a better Electron.
I've also heard good things about the gtk bindings, but I've never really been a fan of classic widget toolkits.
I don't think I'd say any of the rust native libraries are mature: you can do cool things for sure, and they are really interestingly designed, but the polish and breadth isn't there yet. egui is really neat for throwing together a quick tool though.