Comparing organic growth rates is one of the most effective ways to compare 3-D printing investments. Taking it a step further, if you compare a company's organic growth rate against the industry growth rate, it can allow an investor to quickly gauge if a company is gaining or losing market share. contributor Steve Heller compares the organic growth rates of 3D Systems (NYSE:DDD), Stratasys (NASDAQ:SSYS), and ExOne (NASDAQ:XONE), and by this measure determines that 3D Systems remains the best all-around 3-D printing investment. Check out the video below to get the full story.