The question is unclear, but if I'm interpreting it right, you're asking what folks generally use as their first Stadia experience.
While I don't believe there's any hard data to suggest one way or another, I feel the most likely "first experience" people have with Stadia is via the Chrome browser on a PC. I say this because people don't have to buy anything to play on Stadia with this setup -- presumably, they already have a keyboard and a mouse, and possibly even a controller they use for PC games if that's their preferred input method. Now-a-days I imagine that folks are using Android phones as their entry point as, again, they don't have to buy anything now that we have touch controls. From there I imagine some people take the deep dive and purchase the premiere edition to enjoy couch- or bed-based gaming.
This doesn't obviously speak for everyone. I, myself, started with the premiere edition, and just kept buying more CCUs to fill out my house.