it's just Android TV with a different skin on top. really a personal preference as to which one you like more (or a trade-off if you like certain features of one TV over another and one runs Android TV and another runs Google TV)

Both runs on Android TV OS, just different UI

Compared to the old android tv ui I like the new Google tv ui. Especially the left menu vs the top menu. Imo it looks clean. And gives more ui for the content.

They tried to bring some Google tv ui to Android but it's still missing movies/tv tabs which I like because that let me look for movies or tv shows seperately

They are two different things. Google TV is the name of the interface. Android TV is the name of the underlying operating system.

I bought both of my parents Chromecast with Google TV and I just bought a Philips 75in Android TV. The launcher on both are riddled with advertisements. I bought ATV launcher for my TV and it's so much better. Just had to run two adb commands to disable the built in launcher on my TV and it then asks which launcher you want to use. Other than that they are both equally capable. My TV is stuck on Android TV version 9 and I think they are up to version 11 or something. But I have actually tried 11 on my Raspberry Pi4 8Gb and it felt exactly the same with no added features or benefits to speak of so running an "older" version doesn't bother me at all now. IMO they are both equally capable.