Atom vs. RSS
RSS 2.0 is the more widely accepted format for feeds. It is more widely used, primarily because of the fact that WordPress uses it by default. It however, does have a number of drawbacks. RSS does not like XML, and as such, doesn't allow any of it in its content. It is harder to work with than Atom 1.0 because it will only support plain text or HTML.
RSS 2.0 only requires three things for each entry in the feed. It requires: a title, a link, and a description. Other things should be included and required, such as a "last updated" field.
Atom 1.0 is more flexible and has more features than RSS 2.0. It is not as widely accepted as a format for feeds. It requires a link, a title, and a description for each item in the feed, in addition to the feed itself. There is a last updated field, allowing people to see the last time each element in the feed was updated.
Atom 1.0 uses "Autodiscovery." This makes it easier for users and browsers to find and subscribe to feeds.
Atom 1.0 is more secure than RSS 2.0.