I’m a fan of Disqus, personally, and am seriously interested in JS-Kit. Couldn’t get Echo to work properly with my configuration on my own site’s marketing tips blog (www.bluetoquemarketing.com/blog) at the time, though, but am interested in testing it again soon, if there is a simple method of adding it and maintaining it with Joomla.
Also, I am generally a fan, both as a user and as a site designer/writer of the multiple feeds in comments, as long as it doesn’t get too convoluted to look at. Options to turn those things off or hide them, would be a good one for users. The concept is fantastic though, especially with JS-Kit Echo, as it really helps to bring the conversation from across the web into one place.