I had a difficult time choosing between 64gb and 128gb. I currently have a 32gb and have very little storage left, it probably would have been best to go 128gb but it just seemed like a big jump in size.
I've joined the 64GB since iPhone 5 and rarely ran out of space and feel comfortably sitting there just think of this unless you have absolutely loads of pictures and you fancy to store on your phone then be it why not go for twice as much memory for only 100 bucks more as someone already mentioned otherwise I think this much space is not for an average iPhone user.
Had too Sunday morning on line from Apple. All they had left for Friday delivery was 128gb Gold. Maybe some overkill but being a Pro photographer I could make better use of my images and load up the phone a lot more than I do now. So slight overkill but that's okay. I have a 16 now and its pathetic as I have to limit my music and photos. Now I can just load it up