Geforce Now free tier has limitations that make it near unusable without the subscription service. Mostly the one hour session limits, but the queue is inconvenient too. Stadia's free tier limitations is 1080p.
I'm almost 100% convinced that sooner or later Google will start to turn the thumbscrews on the free tier as well, they are not a charity. Either by annoying you with an increasing number of ads or otherwise mining your data, or by technical restrictions that make it almost impossible to enjoy without upgrading to a paid tier. The most likely end game I see is to apply the YouTube model to Stadia as well. So the question is if and for how long Stadia will have that advantage...
