I don't know of too many readers which support only one or the other. With all of the feed parsing frameworks available now, I don't think it's an issue. Are blog developers afraid to pick sides on the RSS vs. Atom debate, or do they expose both formats purely because they can? Take a stand. Simplify your code. From my perspective, providing more than one format for your feed just makes subscribing in Bloglines more complicated than necessary. Then again, Bloglines should be able to tell that the two feeds have identical content and just pick one for me. I wonder if they index both separately or if they have some degree of duplicate detection. Update: Nick answered my question.