Buy stocks. Especially TESLA. They are going to rule the car world. The era of Oil is about to end.
You can alternatively invest in some lithium mining companies, battery/energy companies, solar-cell companies...
I think that making video on youtube or owning website getting paid with Google is the best way and with a low risk.
Low risk and low money... Unless you do something that noone ever done, which won't happen %99.
Buying stocks and being a partner of a successfull company is far more profitable than making a few cents out of google. Since the title asks for the "best investment" and not "the best online job", i assume op has the capital to make an investment.