To decide on this, think about the way in which your prospects normally digest their content.
If you're targeting people who spend most of their time on Instagram, for example, it's clear they are very visual.
A huge long written report is unlikely to resonate with the Instagram crowd.
By the same token, if your target market is used to reading lots of written content quickly, they are unlikely to be enamoured with having to sit through videos.
So do they prefer written content, audio or video?
Your business may be best-suited to offering your time up, or the time of your staff.
Or perhaps you can give them a free tool or software as your lead magnet?
And don't just think of your prospects - it needs to be something which is also best for you.