Look at the software results from our analysis of the UX interaction your current clients have with your current site. We’ll be able to tell you what percentage of your visitors are coming from a mobile device AND if there are more iOS or Android visitors or if there are more smart phone than tablet visitors. Remember, for each version of the responsive design, you’ll have to pay a lot more for that configuration of design layout as there is extensive programming involved to modify the design for different interfaces. The most affordable way to create a mobile-optimized experience on a minimal budget is through viewport tagging. Ultimately, the data from your software results will help you make that decision.