I have to say I am really impressed with Android Auto.
It wasn't even a factor in vehicle purchase, just kind of a bonus. Actually thought it might just be a gimmick, and not much different than simply pairing via bluetooth. But after using it I don't think I would want a car without it (as well as Carplay). I do think Google Assistant is ahead of Siri right now. I use it quite a bit as the recognition is great--I would say better than just using my phone. The OK Google trigger is also very good--definitely better than on my phone. Having it integrated with the vehicle makes a difference, well beyond simple bluetooth pairing. For example, not only just lowering/muting radio sound for voice interaction, but also lowering the climate control fan speed. I haven't even used the built in voice recognition, as I see no need to ever use. I don't even bother with the steering wheel voice button, which will trigger Google Assistant, since OK Google works so well. (Granted it is a little creepy that your car is listening all the time, lol.)
I use it (voice) often for Navigation, setting reminders, replying to messages, and random Google Assitant requests (such as "who starred in x movie").
That said if I switch back to an iPhone, should the iPhone 8 really entice me, I think I would be okay with CarPlay too.
Mike