I am looking to build a report to capture the most popular subject lines by segment. Do you have any recommendations on the type of report and the criteria I should use?
You can create an Email Performance Report with the smart list edited for each segment. Focus on open rates to designate subject line performance. Might have to export a separate report for each segment and compile the results in Excel.
If you have RCE, you can build this out in one report, but if this is a one-time thing it would be simpler to keep it in MA.