Depends on whether your post will get more traffic on its own than within the proper context. For example, this reply would not be better done as a top-post because it only has value within the context of your post.
Also, if the main article was shared on reddit, facebook, and twitter there will be more traffic and voters in this thread which means you can make more by joining an active discussion than attempting to start a new one.
The only time it make sense to start a new thread is if you have enough to say that is context independent to justify a blog post. I have done this a few times. I create a blog post to reply in detail to a question, then I link to my post in the comments.
Voters will decide whether or not your content is in the proper context.