Google is a very mature company with iron control over their monetization, they're in for the long haul. The OP specifically wrote working for google search, which is their core product and that's something that matters when selecting an employer.
Facebook gives me a 'cowboy' feeling and I wouldn't be surprised if in the long term they'll just be another footnote.
I used to think pretty highly of google but their last couple of years have been less then stellar, so I can't see either as a decision without downsides, but overall at least for me google clearly wins out.
Facebook's origins and CEO will forever leave a mark on that company.