It's kind of a chicken and egg situation. The biggest thing businesses need is someone that they trust who has gotten great results for 5-6 of their peer businesses, such that they get recommended to use this person/org and that when they talk to this person/org they know their problems so well and can talk confidently about what the business is dealing with, will need, and can attain.
So, you need to pick the thing where you can get great results for 5-6 businesses and have them as case studies - most likely no one will ask to see the case studies, but it's more about having the internal skill you get from doing them.
Some things that might help you figure that out:
1) Which type of businesses and buyers (i.e. titles/roles/problems) would you pick if you were picking the one that'd make it easiest for you to reach your first 10 customers? For example where do you have practice in selling to a certain type of org or a personal network that includes many of a certain type of buyer in your first degree network
2) Which type of business and buyers do you believe you'll be able to get the best results for?
3) Which type of buyers do you like the most and feel like you can best teach, and where they'll want to listen to you teach them? Businesses (and people in general) like buying from people who have successfully educated them about things that they care about
If there's no obvious answer to the above questions for you, then my suggestion would be to brainstorm your best options, and go try them all out either in parallel or in sequence, and then if one of them seems to work well for you, double down on that one.