Both are equally important to the success of a company. In fact one could easily argue that every department is equally important to a company's success.   Marketing is very important for attracting leads and building awareness but another huge role of marketing is research to understand your buyers. Marketing should develop the strategies on how to sell your products/services so that sales can more effectively move prospects through the sales funnel. Understanding your target market, why they buy, who they are, where to find them, etc. is more important now then ever before. With all that being said it sounds like marketing is more important, but remember strategy is useless without execution; that's where sales comes in. The role of sales should be to quickly quality or disqualify leads and move them from awareness of a need to close. As someone mentioned in an earlier response, they are responsible for generating revene, without which your com