Atom is an order of magnitude more complex and strict standard by people who really love xml in contrast to the really simple and less strict rss 2.0. For example almost everything is optional in rss 2.0 so you can have a reasonable feed for stuff like tweets or linkblogs where there is no obvious title. In contrast atom enforces a title for every item which makes this a messy expirience.
I have implemented rss 2.0 parser faster then understanding the atom specification. Atom can do encode stuff like encode html inline the xml instead of as a CDATA string. In theory this sounds great, but is ends up in a big mess of complexity (e.g. a blogpost with handwritten invalid html).
These days there is also JSONFeed which is really easy to parse, simple and flexible, but it is not supported everywhere yet.
I have implemented rss 2.0 parser faster then understanding the atom specification. Atom can do encode stuff like encode html inline the xml instead of as a CDATA string. In theory this sounds great, but is ends up in a big mess of complexity (e.g. a blogpost with handwritten invalid html).
These days there is also JSONFeed which is really easy to parse, simple and flexible, but it is not supported everywhere yet.