I always check in with Google for this kind of data, specifically their free Search Engine Keyword Tool that’s part of AdWords. The local page ranking search results (in California) are as follows:

  • Flyer design: 18,000
  • Flier design: 390

Interestingly, adding an “s” to the word “design” produces almost flip-flopped Google ranking results:

  • Flyer designs: 3,600
  • Flier designs: 22,200