Many conclusions were drawn from the results of the most recent Steam Hardware and Software survey conducted by Valve, and most of it erroneously concluded which VR headsets were dominating the market, which resulted in missing the bigger picture.
So that you have an idea, Valve conducts a monthly survey on Steam gamers to derive statistics that determine which software and hardware are being utilized by the community and to get a feel on the shifting of trends.
Valve has recently added a "VR headsets" segment to the monthly survey in order to look into which headsets gamers are using on Steam. It's also important to note that while the Oculus Rift is supported by Steam, the official content provider for the said headset is the Oculus Home. Gleaning over the stats, it difficult to come up with the conclusion on which VR headsets gamers are using on Steam.
To recap, there are two major headsets being used on Steam right now, the HTC Vive and the Oculus Rift. Going back to the data set, we can't really say it's totally useless when trying to reference which is the leading headset right now; looking at the graphs for the 2nd quarter of 2016, we can see that the Oculus Rift was able to stymie the growth of the industry-leading HTC Vive. To make this simpler, more and more gamers are gaming online using the Oculus Rift compared to the HTC Vive.
The data is limited though, so we can't jump to a scientifically-backed conclusion. But what we know is that the Rift and the Vive are slugging it out in the PC market, and the PlayStation is soon to make its debut with the PlayStation VR which will launch this coming October. Whatever happens though, it would be beneficial for everybody for all the headsets to be successful. If one of them fails, then it's going to meet fewer choices for the gaming market, and we come out on the losing end.