I have been using Moodle for more than 6 years and have been using Google Classroom in seven of my classes since the start of 2015. Classroom has a great user interface and with Google behind it, it can only get better. However, I did get a distinct impression that Google did not try to learn from Moodle and chose to instead find out the issues the hard way. A lot of the problems I will be mentioning are well-documented and publicly accessible issues (and solutions) that Moodle had to over come. Google chose instead of reinvent the wheel. They are also less transparent (a lot less) on how and when issues will be fixed. Hopefully that will change in the future.
Here are what I think could still be improved in Classroom. They are the reasons why Moodle is still my preferred LMS currently. Note that Classroom gets updated all the time and some of what I say here may already be out of date.
Via Miloš Bajčetić
Une comparaison entre Moodle et Google Classroom