Chinese smartphone giant Xiaomi was valued at $46 billion after its most recent round of funding in late 2014, making it the most valuable start-up in the world. That makes it much bigger than Sony (NYSE: SNE), which has an enterprise value of $31 billion. Xiaomi and Sony now compete in many areas, including mobile devices, wearables, TVs, and smart appliances.But investors might be wondering if Xiaomi, which was founded just six years ago, should really be worth more than Sony, one of the most well-known brands in the world.