For the lingest time it was Command and Conquer Tiberian Sun.
Because our younger self loved the desolate atmosphere and the worldbuilding of tibeberium.
These days it's kinda whatever, but I don't have a particular favorite, I spent a lot of time on Minecraft, I used to try to speedrun super Metroid but I wasn't good at it. I dunno I enjoy a lot of things and then move on instead of one this is my favorite above every else these days.
I love a lot of things though so shrug