When writing the story, use whatever formatting that you, personally, like the best. Then change the formatting to fit wherever you post or publish. And take advantage of Styles.
I use palatino 11 pt because that's what I like - with Styles used for chapter headings, section breaks, etc. Also a macro that toggles between palatino and comic sans (yes, that font) because I like using comic sans when I do revisions.
When a story is finished, I have a macro-aided process to change to Times New Roman, adjust paragraph spacing and indentation, change section breaks, and otherwise fix things for posting to a forum like this one, or on my website, or to make into an ebook.