The answer is..... we cannot answer this questions without knowing the business type and overall goal of the marketing. Then we need to know exactly who your customer is that you are targeting. We would preferably know location they live, age, interest, why they use your product or service, how often they need this product or service, is this group repeat customers or returning customers.
Until you know your customer base and know exactly what the end goal is of the marketing we cannot answer what is the "best" or "most effective". In my business I know my customer is within a 10 mile targeted area, over 51 years of age, thinking about retirement, highly likely to be an employee and not a business owner to name a few things.
Other things that need to taken into account is push vs pull marketing. Understand what type of marketing Facebook, Twitter, and Instagram are when compared to Google Adwords and know how to effectively use their best use.