Pokemon definetly is my most precious, dearest and direst time sink
I played the oldest ones, Blue and Gold for a pretty long while, 200+ hours I think
I sunk over 500 on Sapphire and LeafGreen respectively on consecutive playthroughs
Diamond, Platinum and Heart Goldained even more hours: 300+ on Diamond, 500+ on Platinum and most likely, over 800 on Heart Gold
Y was later when I became strictly a competitive player, but still I clocked in at over 650 at the game's inner clock
Last but not least, Black and Black 2 was at a time when I got into competitive while still having the joy of starting all over again and that went on for almost two years and it still does, sometimes. I probably have over 1700+ hours in Black 2 by its own
As a final note, the hacks and fangames have done all of this to an extent, but never surpassing 400-hour mark and Showdown has sucked far over 1000 hours from me
Now that I think of it, maybe this is the reason why I never got into MMOs; I already have a time-sink of my own