I think stories nicely formatted into paragraphs with only one blank line between each paragraph are the most readable. However, I have yet to hit upon a consistent way to do it.
I write my stories offline and end each paragraph followed by one blank line. When the story is published, it ends up with 2-3 blank lines after each paragraph.
What is the trick?
I really wish we were able to reformat/revise and correct spelling/grammar on our own stories after publishing (just like we can edit posts in the forum). Yes I am anal about these things.