When I try to resolve an edit conflict, I want to quickly scan through the columns. If the texts are perfectly aligned I can easily scan through the lines.
Make sure that the //width of the text lines// is exactly the same for both columns. This means:
* If the text is in one of the changes boxes, and thus preceded by a vertical line, it still does not have a smaller length,but exactly the same as the editor
* If the text is not in one of the changes boxes, it is also exactly as long as in the editor, even if that means that the text column on the left has slightly different widths for separate lines
Also make sure the //spacing// between the lines is the same between editor and text column, at least for the most used browser type with no special settings ([[ https://analytics.wikimedia.org/dashboards/browsers/#all-sites-by-browser | which is chrome according to the WMF ]])