My favorite is blogging, when I started internet marketing I was taught different ways to make money online but I just fell in love with blogging. It looked easy for me and it appeared to be a long term strategy (which it is).
And blog posts can go viral pretty easy, just as long as they're good quality, informative or really entertaining. A blog is also versatile, it gives you a lot of ways to monetize, build a loyal following and email list. With blogging I get traffic, email subscribers and sales every day, whether I'm working or not so that is why I love it
I also get to be an authority in my niche/market and that reputation has a lot of benefits.