Xiaomi Mi A-series Are The Best Selling Android One phones
The Mi A-series are exclusively Android One smartphones. That means the competition are primarily Nokia and Motorola smartphones, as those are the only other two major smartphone brands that are invested in the Android One project.
Here is a pictorial chart from Xiaomi of how Android One did in 2018:
Xiaomi says they have sold more than 10 million units of the Mi A-series worldwide, and hinted that their next Mi A-series device will sport a 48 megapixel camera.