Apple is probably top dog here... they made more in profits than Google's total revenue for 2010 Q4.
sources: - http://www.mercurynews.com/business/ci_17152005 - http://www.bloomberg.com/news/2011-01-18/apple-profit-rises-...
Facebook does, at least in the sense that both operate in the web/user space, and both have advertising as their fundamental source of revenue.
Apple & Google are both pretty big companies and will likely be competing in the same space given the number of products they both own. Apple's iAds are a direct competitor to Adsense on mobile devices, Apple TV/Google TV, etc.