It hurts to hear people ask that question, and others like it (what can I blog/podcast/sell) that makes the most money?
You are asking the wrong question if you want to make money.
Ask this: "What value can I provide to a group (people/businesses/pets/whatever) that is so useful/entertaining/removes pain point/etc that the group I'm targeting above will be willing to pay me money?
I recommend reading or at least listening to the audio book version of "Unscripted", by MJ Demarco.