Collectively, the top 10 trending videos for 2017 have more than 633 million views and have been watched for over 40 million hours. The channels behind the top trending videos have more than 55 million subscribers in total.
The most popular videos on YouTube each year are seldom the most interesting. I find that the videos that are mildly popular, say with single millions of views or hundreds of thousands of views, are the most interesting to me. They have a broad enough audience that the creator is getting paid well and they generally are not flashes in the pan.