I had plenty of space on my 64gb but as time has gone on, not so much (about 7gb free). I'll get the 128gb next time.
That's the problem with phones lacking a memory card slot. For six years with Android, I refused to get a phone without one. My last phone was a 32GB HTC One M8, and I had a 64GB card in it. So 96GB total. I had Nandroid (full system) backups, Titanium backups (apps and their settings — yes, this was somewhat redundant), and a bunch of other crap I didn't need, but I never felt like I had too little space. $30 128GB memory cards didn't even begin to tempt me. Still, I decided that 64GB wouldn't be enough. 96GB was fine. When the Nexus phones came out with the 128GB size (I think Apple had this with the first iPhone 6 but I'm not sure), I thought, I could go without a memory card slot if I had 128GB. And when I went to get my iPhone 6s, I planned to get the 64GB. Figured, without the Nandroids and Titanium backups, 64GB would be enough. And maybe it would be. But you can't get more space on a fixed storage phone like the iPhone or Nexus. But Nexus phones, like any Android phones, are disposable. They don't hold up more than 18-30 months, at least in my experience. Others keep 'em longer but I never did. 24 months was the longest I ever kept one and I had to. I'm thinking, and I hope I'm right, that I'll keep my iPhone 6s for 3-4 years. I know some iPhone 4s users are going on five years with theirs, and that's a 4s (first iPhone I considered owning was the 5s, for widescreen and Touch ID and the specs didn't turn me off, though I realize now they matter less here).
Now what I'm wondering, having fallen in love with the smaller size, if there'll be an SE-sized iPhone when I decide to replace my 6s. No one can really say now, but the SE topping out at 64GB was kind of a disappointment. When I do decide to trade up, if there's a 4" iPhone with the specs of the current ones, with 128GB storage, that's what I want next. Done with big phones. Wife's got a Droid Turbo 2 and it seems huge, though it's only, I think, 5.3". It's a beautiful phone, too, it's just so big. But, it's really not big enough to watch a movie on. It doesn't have a kickstand either, and the back is way too pretty to stick a Flygrip, or a Flygrip and case, on, though the latter would work in a pinch. For all the things a bigger screen would do for me, I'd rather have a laptop, or a notebook, or whatever they're called now. Maybe a MacBook, even. I've only ever used Windows, but only because I'm a gamer. Either I'm getting a gaming laptop, or I'm not, and if I'm not, why suffer Windows? OS X, or, sorry, macOS, is just so much nicer.