Just a quick note: You can import your Wordpress comments into Disqus.
Good to know. If I ever had to use a hosted comments solution like Disqus, I think I would start out with Disqus. Why? They have the most tools to import your old comments AND most other hosted comments services will import from Disqus.
So start with Disqus, see how much it is actually used and if need be you can always move to another service.