Andrew, who designed and hosts my site for me, writes:
The built in WP comments system does a serviceable job, but it could be easier for people to interact–especially since so many come from RSS aggregators.
Both let you add Facebook and Twitter logins for commenters. They both also add email notifications and reply by email. They work on top of WP comments and sync with the WP database. Disqus is more focused on building a community of comments across the web while Intense Debate tries to create a system of “reputation” among commenters.
I’m fairly cautious about major changes, especially to unfamiliar technology, but thought I would open it up to the people who actually make comments. Please let me know.