For a lot of us it will probably end up being some MMORPG or multiplayer FPS. For me there were predominantly 4 phases:
1- Younger me (School) got hooked on Unreal Tournament and UT2004, tried to play other games but they all felt slow. I needed quick games that I could start and finish while being able to do my studies.
2- Slightly older me (undergrad) then got hooked on FF14 online, played that for a few years and nothing else. Had a lot more time after lectures to invest into this hobby and a MMO just helped scratch that itch.
3- An even older me (postgrad) then got hooked onto Neverwinter and basically predominantly just played that. As before I had time after my lab work to spend gaming in the evenings and weekends, so continued with the MMO genre.
4- The even even older me (work/family life) is now a mixed bag and am no longer predominantly playing just one game. I do however require the games to be entertaining very quickly. If a game doesn't hook me within the first couple of hour or so, I basically stop playing and delete it. I do have my "staple" of 3 games that I always fall back on (Apex legends, Rocket leagues, Destiny 2) when not playing the latest and greatest releases (Demons Souls, Control, and soon R&C) .