Hardware(shield), but instead of arduino hardware look into onion's omega project. This looks like a very good investment and also if you start making good shields for the omega(cause no one else is) many MANY people would buy that. About 15,000 people (with about $600,000) have backed the omega2, which is their newest product, on kickstarter. https://www.kickstarter.com/projects/onion/omega2-5-iot-computer-with-wi-fi-powered-by-linux