An RSS feed which takes me to the comment page of the submission.
Reason being that I like to use live bookmarks in Firefox, and the RSS feed which goes directly to the submitted link means if I want to read the comments left by HN users, I must go to HN's homepage to look for the article, and then click on comments.
Which is a lot of work compared to clicking on the live bookmark entry, then opening up the submitted webpage (in a new tab) from the submission's comment page.
