128GB. I have the 64GB iPhone 5 at the moment. I have a lot of music and with kids a lot of photos, video, Ordnance Survey maps for walking and cycling one of which is 3GB and sailing charts. Even though I am moving towards using Spotify I still prefer to have music on my device for when I have poor coverage.
People think I am crazy at work for needing 128GB but we all have different needs. Then again I think it is crazy that people buy smartphones and all they use them for is texting, Facebook and photos.