Building a website is the first kind of business that you can create when looking to start an internet business in a particular niche in the market. Many people have done this with a micro niche, building a website and then profiting off of this small but profitable match. Google is a great place to find more information on this.
There are many choice and I think we can't say the best one. It's depend on your interest and skill.
Making website and monetizing them is still more easier. But selling product is good too for some people. Again, it still depend on your choice.
According to me the most profitable internet business is providing the services on the internet .
Other may be the posting the blogs and the articles submission.
Using the facebook and twitter are also the best for the online money.