How are people adding public comments to their Craft sites? It's not been asked as a broad question here yet, but we've all wondered: how does one go adding comments to a Craft site, such as those you'd find on a blog?

I've either used or been aware of...


Tacking Disqus (JavaScript) comments onto pages. 
Integrating Google+ comments.
Using a dedicated Craft Section for comments and relating each to a post, collecting submissions with Guest Entries.


Are there others out there? Would an expert comment engineer care to answer authoritatively?
What you describe above is essentially your options. If you use built in sections for comments, you can probably make them more secure from spam by using Dukt's OAuth plugin to require a log in from a more reputable site.

Other third-party options include:


Intense Debate (from the makers of WordPress)
LiveFyre Comments
Facebook Comments