When it comes to which devices are considered the "best smartphones," that description can have a very different meaning to many people. When you look at the world's top smartphone manufacturers, it's clear that those at the very top must be doing something right as they're continuing to dominate the market, regardless of whether or not they're looked at as the best. Xiaomi is one of these companies as they've been growing rapidly over the last couple of years. Xiaomi as a brand is only a mere four years old, but that hasn't stopped them from achieving massive growth leading them to become China's number one smartphone OEM.
They're currently valued by investors at a cool $45 billion, an amazing feat for such a short period of time, and Xiaomi only aims to go up from here. They're already dominating the market in China among the big players like Samsung and Apple, which is quite an accomplishment considering Apple's brand recognition. Although when you consider the cost of Xiaomi's phones compared to an iPhone in China and other emerging markets, it's easy to see how they have risen above their competitors. Some have considered Xiaomi nothing more than an Apple clone, and while it may be true that they have taken heavy influences and inspiration from the Cupertino based corporation, they still do things quite differently, like with their sales model for devices which they only sell through flash sales online in small batches and short time periods.
There's no other way to describe it except to say that Xiaomi's growth has been explosive, and so much so that Tim Cook even referred to Xiaomi as stiff competition at a talk with Goldman Sachs during a technology conference. He led into that statement by saying that he doesn't worry about Xiaomi, and that he doesn't "lose sleep over them," but having the most valuable company in the world recognize a four year old startup as competition is something to be proud of, and the very reason that Apple is likely having to watch them closely. They may not lose any sleep over Xiaomi, but they are more than likely paying very close attention to their movements.