It all depends on your target market and the type of clients you're wanting to attract. Google Adwords, Bing and even Facebook and LinkedIn all have a place at the table when it comes to marketing.
What we've found with much of the clients we work with is that lesser technology type clients deal more with Bing than with Google. That said, many corporations, schools and medical facilities REQUIRE Internet Explorer by users, and many of the staff utilize Bing in those cases too.
If you're targeting Wix and SquareSpace type users that are looking for DIY and drag and drop, then Bing is a great place for clients. If you're looking to target programmers and developers, then Google is your friend.
If you're looking to target startups, DIY'ers trying to launch a business etc - Facebook can be a winfall.
Do the research. Find your target and who it is that you're really looking for, and at what price point. Then test, repeat, test, then launch.