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 the end user the biggest advantage it that you don't have to create a separate account for each site, you can comment using an existing Disqus account. It really saves a lot of time for the end user as well. Comment moderation is also simple, Disqus has a very nice user interface for moderation.