All are correct, depending on the style you choose. While many absolute rules govern spelling and punctuation, much of style is governed by convention. Writers and editors choose whether a word will get a hyphen, a capital or be followed by a comma. These conventions vary depending on the purpose of the document, the audience and the organization.
Fiction writers think of style as the writer's voice or use of language.
Designers think of style as the layout and format of a document. In print documents, attending to style is an expected phase of the publication process. But in the online world, style considerations are often overlooked in the rush to post timely content. The result is the editorial equivalent of mismatched socks. A lot of online writing makes a poor impression.