17.4 GB of material between pictures, music, apps, etc. This is my first 64GB and I will be going with this option going forward. That peace of mind is nice to know that you have the space on your phone.
I have a 32GB 5s and I'm almost always running out of space; currently I'm at 900MB free since I did some "cleaning up" earlier. I usually have to look through apps and pictures to see what I can do without. I usually delete my music library since I have iTunes Match and that streams without downloading locally and taking up space. My Photos take up about 12GB of my space and Messages about 4GB. The rest are just apps and stuff.
I have a friend who has a 64GB 5s and she's worse off than me; she's usually in the double digits (in MB) when it comes to available space. She loves taking pictures and videos, which she combs through and delete when she needs the space.
I've gotta lot of space left on my 32GB, but that's because ALL (I mean all) of my photos are in iCloud photo drive. If I didn't have that, then I would need a 64GB Phone to combine my iPod and Phone