I have a 200GB and it's almost full. But keep in mind that I have a lot of movies and TV shows on that card. And I play multiple games at the same time (like 2 puzzle games, 1 rpg, 1 fighting, 1 horror game and whatever) and also keep any multiplayer game on there indefinitely just in case I hang out with friends.
It really depends on how many games you want to have with you.