Configure the settings for a content type

1. Click Administer > Content Management > Content Types.
2. Click a content type.
3. In the Comment Settings area specify any of the following settings.

Viewing options

• Display Mode Collapsed or Expanded? Collapsed breaks every comment out onto its own page. I don't think it is a good idea. It makes very hard to follow the conversation. I would rather use Expanded.
  
  Threaded means comments are connected to each others. They remains no longer in chronological order. According to my experiences users don't use it properly. So I recommend Flat List, which is much simpler.
• Default Display Order- I wouldn't recommend "Oldest first" and "Newest first" either. It is up to you.
• Comments Control-It depends on your website's users. For the most cases, I would use "Do not display." It is the safest, so users can't destroy the settings you have done.
• Comments Per Pages-Default number of comments for each page. Small number means faster page display. If you use oldest first, I recomend set this value as high as possible. So that your comments will be listed on a single page.

Posting Settings

• Anonymous Commenting- Anonym comments are faster and more effective. Nobody wants to register only to post a single comment. But it can be dangerous. There will allways be someone who's going to abuse with your trust. If you are unguarded, spams can flood your website quite fast.
• Subject Field- Comments are quite short, so I think there is no need to complicate the posting by requiring Subject. But Drupal uses it in the comment block, and in many other places. If you would like to favor your users do not require subject. If you would like your website to look well, require subjects.
• Preview Comment- From security's point of view, it is a good defence against spams to require preview. For usability standpoint it is just an additional page, and what's more, some users may confuse. I would only use preview if spams cause a lot of problem.
• Location of Comment Form- It depends on the design of your website. If long pages don't mean problem, I recomend using "Display below post or comments".