u/Glad_Armadillo_5788

Personally I would ether choose season 7 or 8, season 7 had the leviathans who were pretty much another apocalypse and with how it end with Dean going to purgatory you could have it be Dean sacrificing himself and Sam having to live it with it, similar with 8, while the main plot isn’t necessarily a apocalypse issue, the finale is very emotional and Sam was sacrificing himself like he did in season 5, so I think these two would be where I would end it.