Affiliate marketing and writing articles is a great way to start making money on the interne (thats why sites like hubpages are so popular!). But you said "most profitable, and successful type of business", and I wouldn't recommend you spend all your time writing articles as a business model.
Doing this, you're basically sending all your traffic and hard hours to someones bank account, not yours. If you want a long term successful online business, you need to have a solid website where you...
1) offer product/services for purchasing
2) create an email list that will generate you continuous income
I have years of experience in growing online businesses, and my website has lots of resources specifically for entrepreneurs who want to create a solid website online (see my profile for link), I hope my advice has helped!