Those who follow LeaseCosts articles will know we love the videos from Jakub & Jury, from the Straight Pipes. So, without trying to go directly to any "system-specific" comparison, as they do it pretty well, I will just leave their two most recent videos. The first one is from March 2017 and the 2nd one from just a few days ago, in January 2018.
Main tests: Voice Control, Maps, Messaging and Voice Recognition.
Android Auto vs. Apple CarPlay Round 1 (March 2017)
Android Auto vs. Apple CarPlay Round 2 (January 2018)
Android Auto vs. Apple CarPlay Round 3 (Sep 2018)
Android Auto vs. Apple CarPlay Round 4 (July 2019)
Android Auto vs. Apple CarPlay Round 5 (Oct 2019)
Extra: Lauren Goode from The Verge
Lauren Goode, Senior Tech Editor from The Verge, has this very introductory video for presenting and slightly comparing both technologies. It was published back in 2016 when both systems were initially launched, but good enough to onboard yourself on the general aspects of Android Auto and Apple CarPlay.