I used both. When time came to Play cyberpunk, I went for Stadia.

It runs a lot better (streaming quality, glitches, start-up times) are incredible. Using Stadia in general is a polished (yet basic) experience. In contrast Nvidia very much felt like a hack. Log-in in my steam account, seeing weird window glitches.

I see a lot of comments negative on stadia here,based on bias rather then actual experience. Stadia is nothing short of tech star even with its downsides compare to the rest of the market.