The problem with sorting comments by best is an early so called best comment gets stuck on top and gets seen by more people therefor artificially gets more likes. If someone makes a much better comment later on it never has a chance because it is pushed down out of sight. I see this on YouTube and Disqus all the time when sort by best is the default setting. The “best” comment is good enough to get upvotes but really is not the best, its not even that good, it just had the advantage of getting more views because it rose to the top early on. I think sort by newest as default encourages the longest discussions because I feel like if my comment has 100 above it few people are going to read down that far so why bother.