Vitaly Tennant compared the IntenseDebate, Disqus, Livefyre and WordPress comment platforms in this post.
A major Disqus issue you should be aware of when choosing a commenting platform is that visitors that are blocking Google Analytics (In their personal firewall or another privacy program) will not be able to load the Disqus code [on your site] if Google Analytics integration is enabled in [your] Disqus [settings].
As a growing number of people are becoming more and more aware of the privacy risks they face online, site owners should take this into consideration. If a visitor is blocking Google Analytics, that's no great loss to you. The visitor can still read your content and interact with your site. He can still post comments and buy products and do all the other things a visitor usually does. If however you are closely integrating Google Analytics into your site, like the people at Disqus have done, you are making parts of your site unavailable to people with enhanced privacy settings. In the best case, they merely won't be able to comment on your blog. In the worst case, you are scaring off potential customers or preventing them from buying your products.