TBH, I have a love / hate relationship with Apple Car play (ACP). From a speed and just "working" point of view, it's much better than Android auto (IMO). Loading of it after attaching the USB cable is pretty much instant (once the Nav unit has fully booted), and streaming from say Tune-In radio starts very quickly. Conversely with Android Auto (AA), it can take up to 10-15 seconds (usually about 10 secs) for it to start then you have to acknowledge a nag screen, and streaming from Tune-In seems to take longer to achieve a connection. Also, I've found that ACP seems to always work 1st time every time, whereas occasionally AA either won't start or crashes (not that often to be fair but enough), requiring either the phone to be unplugged or the Nav unit re-booting.
AA is great when you are doing quite a lengthy journey and you only need to connect once at the start of your drive, but if you need to stop a few times, it can get really annoying waiting for AA to start up (although it does seem a lot of the time is the Nav Pro unit waiting to start the app connect service on engine re-start.)
For me though the big turn off on ACP is the screen design, which whilst I know it's supposed to be safe and easy to read when driving, looks like it was designed by a 2 year old. God knows why they thought to have album art behind the next as it blurred to such a point as being totally worthless. Then you have the Apple ring fence on apps, which can be a good or bad thing. Good in that only apps that have been fully tested are allowed though, bad in that it only shows you what Apple deems you need.
AA on the other hand being is much more flexible and just plain looks better on screen. When I play Tune-In or Spotify, I get a really nicely presented screen with cover art (displayed properly) and easy to read text that isn't 6" tall - and yet it's all still perfectly readable at a glance, and therefore just as safe as ACP.
Add to that some of the other apps you can get such as Google maps and Waze (and other not officially supported apps as well is you allow you phone to go into developer mode). For me, the real bugger however with both these apps is that they both disable Bluetooth when connected. So if like me you have two phones (one Iphone - Work and one Android Personal) connected at the same time to the head unit, you will loose connect to the other one when the respective app has loaded (so when ACP is loaded, my Iphone still receives calls in the car, but my Galaxy S7 doesn't, and vice-versa.) So it sun it up for me ACP has the speed and stability, and AA has the looks and features. If we could combine the best of both, what an App we would have !