The big advantage Stadia has over GeForce Now is that for GeForce Now you have to have a machine capable of playing those games in the first place. If you have a great gaming PC, then Stadia probably isn't for you.
Edit: I was mistaken. i was thinking on nVidia GameStream feature that allows you to stream from your PC to Shiled in your home.
Edit: I was mistaken. i was thinking on nVidia GameStream feature that allows you to stream from your PC to Shiled in your home.