Exactly, this is a factor of who your targeted audience is, which type of people do you want to get your message, then a research on the preferred social media network of them will now determine the particular one you will go in forIt depends on the target audience and the products/requirements.
If you are looking for a good professional in IT field or some other field, LinkedIn is the best place for that and you can place ads, listing your requirements. If you are trying to sell a niche product, then try to look for those particular groups in Facebook or Twitter and contact the owner about the marketing ads. There are many social media platforms out there and you can take your pick. Good luck!