I would have said Undertale. But I think, after beating the True Pacifist Route and getting the ending. I think I'm just gonna leave it, and move on. I'm perfectly content leaving everything as it is, and letting Frisk be happy.
So ultimately, I don't think I'm going to reset everything and do genocide.
I'll probably move on to some other games, I have plenty of Steam games that I bought but haven't played yet. Maybe... Doorkickers?