Which elsarticle documentclass parameters in LaTeX should I use for different Elsevier journals?
The options not only allow you to chose between three different two-column layouts but also one column modes. The role of the two-column mode is to allow the journal to type-set the article once it should be published. You can therefore use the settings to to see the length of your final article (in terms of journal pages. In other words, you as an author have access to the type-setting mode of the journal paper, this is a side-effect of the versatility of LaTeX class construction in the manuscript handling phase. 

The fact that there are no instructions for which to use means you can chose whichever suits the format best. I am, however, sure the journal can take the final manuscript in any of the modes since the only thing they need to do is to switch a comment between two lines if your choice is not optimal. I would send in the manuscript in single-column format and let the journal worry about which of the formats they use in the end.