Its not as simple to know “what is the most profitable” as you make out.
Do you have the stock to run a successful Ecommerce store?
Do you have the money to invest into servers, a support team, advertising etc for a hosting company?
Do you have the resources to make a fully blown google style search engine?
Are you a good enough, competent enough graphic designer to do it for a living?
Do you know enough about music to run a successful music website?
Each one of these websites will require an initial investment as well as constant work updating and maintaining.
Obviously a successful ecommerce website is going to be more profitable than an unsuccessful search engine.
Take a step, work out what you actually want to do, then do it. Don’t feel limited by what other people say is the “most profitable”.
Hope that helps, Good luck with your project.