I think earning money online from Google Adsense is not only the best but the easiest option for anyone who can write well on a topic or maintain a website.
It is one of the easiest option for a beginner who can join Hubpage or similar site or start a blog on a subject of his/her interest and start making money. There is no need to be a marketer. There is no investment, although earnings are not that good but its a risk free option.
Google Adsense is also good for those who love to concentrate on a single job, like making there site useful for visitors, with adsense they can do there job, as adsense will do its on its own.
If we look at the stats of people who are making money online (small or big) we'll find that more than 90% make money from Google Adsense. Failure rates with Adsense are also very low as every one earns something for his/her efforts.