Team Fortress 2, with over 2100 hours logged. More back on the Xbox 360 copy and when it was free during the Mac Update.
Tf2 too for me. I played almost 5000 hrs. Not counting two side accounts I made for collecting halloween stuff/ playing incognito. Played some etf2l and went to some lans. Was a good time!
CS:GO, followed quite closely KSP.
Although Super Monkey Ball 2 on GameCube I suspect handily beats either.... but I can't track it lmao.
In my old gamer life probably Mario Kart 64 in my new gamer life I restarted after working Endless Space 2 or Go/Baduk (if you some up all clients for that game)
If we just talk about the last few years:
There is a soft spot in my heart for SuperTuxKart too, despite the current project leadership.
yoo i tried xonotic for the 1st time today, was absolutely epic. also tell me more about the supertuxkart situation?