So I believe we are at a virtual crossroads so to speak, where a case could be made for any of these games being the "biggest" shooter at the moment. There are so many measures (media coverage, streamers and viewers, scores and metas, competitive scenes etc) you could use that I think it would make for an interesting discussion.
So in short: which do you think is the biggest shooter at the moment and do you believe it will change in the coming years?