I have a 3GS that I'm (mostly) happy with. But my wife's phone is dying fast, and she'd like the 3GS. Which leaves me to upgrade. As evidenced by the old phone, I generally keep my devices for quite some time. I'm torn between going for the 6s (best stats, will last longest) and worrying about the battery life. Would I be better to go with a 5s/6? Or bite the bullet and get a 6s 64?