Also! If you want, you can give an explanation in the comments why you think that victory is the Hardest. (Note: All of you comments are opinion and I don't want anyone fighting over their own opinions down here, so if so if you disagree with another persons opinion then just agree to disagree with them, ok?)

I personally think that a culture victory is by far the hardest victory type since most of the tie you will be heading into the late game before you even get close to acquiring this, and at that point the culture required will be unnecessary. (I am playing a culture victory as of writing this. (Settings: Nzinga Mbande, Standard size (Continents and Islands), Prince, 14 City states, No game modes, Infinite turns, no score victory, no diplomatic victory))