What to use to grow your business depends a great deal on what you want to sell, what your budget is, and how well you've optimized your funnel.
Oh, and where to send your traffic? To opt-in pages first and foremost, so you can build your list. Then send them to an irresistible offer, and maybe another offer from there. if your funnel works well (see above), you may be able to afford more advertising since it hopefully pays for itself.
For growing my business and getting more traffic, I personally focus on blogging first, along with Facebook traffic and promoted posts. A press release here and there can also help. Haven't had much of a response with Twitter though, plus their ads are not exactly a great deal. Facebook ads are better, once you know how to optimize them.