Options:

{{{
== header ==
== header
!! header
h2. header
}}}

Using equal signs (=) is the most popular wiki header markup. Since there are more equal signs for smaller headers, subheaders will become more indented making it easier to get a visual overview from the markup alone. Closing equal signs are optional, making Creole more flexible since many wiki engines do not use them.

There was a complaint for exclamation points (!!) that they do not indent further headers, making it difficult to keep an overview of the document content.

Syntax like h2. looks too much like HTML.