I agree with Eva: giving us the option for each individual FreeSpace page would be the best of both worlds.
At the default font and typeface size on a full desktop or laptop display (assuming at least a 1280 horizontal resolution; 1920 is more common nowadays), a single line of text in single column on a FreeSpace page would be approximately 150 characters long, including spaces. Typical for optimum readability (think Microsoft Word with the out-of-the-box defaults) is about two-thirds that, or 95 to 100 characters. Long paragraphs of text will be more difficult to read because the eye is having to track too far to the right of the line-start to return easily to the subsequent line.
Even using <blockquote> would (I believe) give us a 130-character line, so only a little help. If we could use CSS formatting for margins on a FreeSpace page, that would allow more optimally readable lines in a single-column presentation (e.g., <div style="margin-left:10rem; margin-right:10rem;"> which would result in about 100 characters). But that's not likely because, though "rem" adjusts responsively for the size of the viewing device, it could still be a problem at small cell-phone size; and it would present a geeky learning curve, anyway.
I agree with Emma that a one-column layout gives much better spread for data presented in tabular form, and for graphics that would otherwise require a separate click to be legible full size.
So I see the best solution is to let the individual choose the layout. Mostly paragraphs of text, two-column is likely preferrable. Big tables and large images, single-column.