there is no best alternative as Google owns more than 80% of overall market. If you want scale you cannot ignore Google - hence the monopoly and inflation of bid rates.
the next best alternative which can bring 1/4th of google adwords traffic are bing adcenter, retargeting companies like adroll, vizury.
Facebook & Linked Ads work for specific domains.
the next best alternative which can bring 1/4th of google adwords traffic are bing adcenter, retargeting companies like adroll, vizury. Facebook & Linked Ads work for specific domains.