Absolutely Google... but over the past 12 months we have seen a upward trend in Search Alliance (Bing/Yahoo) where I'm seeing good return and high Value to Cost Ratio's for my clients (especially eCommerce). Bing Shopping leaves much to be desired, but they, it seems, are migrating to a paid version just the same as G is with the exception of the fact that they are utilizing Shopping.com for product feeds (only for certain cats right now, but can't see why this wouldn't be a complete migration in the future).
CPCs were almost invariably lower – and usually significantly lower – on YBN than AdWords – from 37 to 77 percent of AdWords' CPCs, again varying by vertical. So, advertisers were paying a high premium to gain access to AdWords' heartier search traffic and CTRs. And, as a result of lower CPCs, Brand Impressions (first SERP CPMs) varied from 76 to 90 percent cheaper, on average, on YBN than on AdWords.