I’ve been using Disqus as the commenting system on one of my major Wordpress sites for years. I am naming Disqus the Cool Tech of the Week this week due to a new feature they just released - Disqus Recommendations
Disqus has always provided a nice upgrade to the default Wordpress commenting system and I have found the plug-in works well, has great moderation and setting features.
The new recommendations feature provides a nice way to cross promote the different blog posts on your site which is something always useful to keep users on your site (increases dwell time and conversion potential).
Check out Disqus, they have changed a lot in their pricing structure since I started with them. The free version is ad supported, but any of the paid options are ad free.