I think they're pretty even now for the user, but Stadia has some pretty big business advantages long term that may already be evident in that GeForce Now has queues and Stadia doesn't. The main thing is Nvidia probably doesn't have as much work it can do on machines that aren't being used, whereas the Stadia machines can probably be doing useful work even when the gamers are all sleeping. Stadia can therefore justify having way more capacity than is usually needed, which means having more machines closer to users (lower latency) and being able to deal with peaks better. For everything cloud-related, scale is such a big advantage it seems like it'll be hard long term for Nvidia to compete with Microsoft, Amazon, or Google.

Stadia also doesn't have to pay the Windows tax