It just depends on you as a player. Do you still find the taken King fun? Are you going to be playing a lot of destiny still? Are you still grinding for certain weapons and gear? The taken King dlc is already here and there is a confirmed update coming in December for new and updated exotics. Buying the black ops 3 dlc only gives you the giant and your still gonna wait another 2 months before the first dlc comes out sometime in late January.