Few months back I started using disqus commenting system on my site, so far my experience is good. Disqus is very is easy in install and configure. Download and install disqus module from Drupal.org enable it, get api key for your site from Disqus.com and that's it.
For end user the biggest advantage it that you don't have to create separate account for each site, you can comment using existing disqus account. It really save a lot of time for end user as well.