Some people think youtube comments are complete trash. They usually watch videos of very large channels. Other people think youtube comments are dull but not particularly horrible but rarely insightful. It's common to hear this about channels with a million subscribers or less. But below 100,000 subscribers, in the long-tail of youtube, you'll often find that content creators enjoy having reasonably constructive conversations with their viewers in the comments.

There are always exceptions, but these are the general trends I've noticed.

Examples of the first category, the very large channels, are easy to find. Pewdiepie, and anybody like him, have awful comment sections and I think everybody knows it. I subscribe to several very small channels with only hundreds or thousands of subscribers that have great comment sections, but you'll have to excuse me for not sharing them here. In the middle range, I can give you a few examples. Matthias Wandel (woodworking) and Forgotten Weapons (history and overview of rare/historical firearms) both recently passed 1 million. Their comment sections are rarely insightful, but typically not offensively bad. Mostly just people making the same obvious joke over and over again, or people trying and failing to be insightful.