Well, it's hard to define the exact one and name it as the best one. When it meets your needs, tells your audience about your product and how to use it, draw an attention and interest, then it's the best one for you. If it's not, you'll need to try another one. For some projects, for example, mobile apps, I would say video ad is the most beneficial. If you want to know about different forms of advertising and how they works, I'd recommend you to check out blog of Smartyads company.