What is the top marketing company that markets online websites?

I am going to start an online business soon and I would like to advertise online. However, there are tons of companies out there that say they can get me hits on my website and can get me at the top of search engines. I don't have the money, time or resources to try each one, however, if anyone knows of any marketing companies that has a proven track record, I would be oblige to know.

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