I would start with what you know as long as its economical for you. Trying to get into business selling products for the wrong reasons (i.e. just because its popular) usually doesn’t work out well for people. You should start selling something that you are into or that you already know a lot about.
If you don’t sell a product, there are a lot of other ways you can make money online. Keep in mind that the internet is just a channel and not the main function of making money. You still have to be doing something that you are good at in order to be successful. For example if you like writing there are a lot of content providers looking for writers out there. You can create a profile on sites like elance and bid for jobs.
Hope that helps,