~ Online Business - Type of Business ~

I think this is a very important question to not only myself, but for our audience.

Starting an online business, assuming I'm in the "providing a service or special interest" to a client, What is your opinion regarding the following question?

What "type" of online business is the most financially lucrative business model to pursue? (Product/Service/Video/Photo/Blog/Writing?)

I know this is a very broad range and impossible to give an exact answer so be open-minded and just express yourself. (I sound like Madonna, but don't share her vocal talents)