As of December 2017, Vive has a market share of 47.26%. Facebook's Oculus Rift has a market share of 46.14%, with Microsoft's Mixed Reality entering the market, Score 4%.
However, it's worth noting that, despite the large number of Vive users, Steam still listed the Oculus Rift as the most popular VR device in December, the first time Rift has beaten Vivie, though the difference is only 0.17%. The definition of popular devices is not published.