If by format you mean doc, ebook, powerpoint, video or audio, the answer is all of them. That will give you the widest reach and it's fairly easy to do with free software. Start with the text to map out the course then add that to powerpoint. Make a screen recording of you running through the powerpoint slides. Extract the audio from the video. By the end you should have a transcript, powerpoint, audio and a video version. You can package these separately then bundle them together or split them at at different price points (always stacking the deal towards the full bundle). This will give you the greatest reach across platforms and higher product value. To extend this you would add the buyers to an email list and continue to market to them into the future. As the saying goes, the money is in the list.