It would depend on what you are doing with it. Screen time, I would say that the Nexus 5 is a little better but standby time on the iPhone is better. If you are a person who does mostly texting, emailing, calls, maybe some music, but not much else, the iPhone will give you great battery life. On my work days I usually come home after 10 hours with about 75 percent because I usually just text and make a few phone calls and send out some emails. But if I start watching videos, the battery will drain fast. Same with games. The Nexus is constantly processing thing a in the background so the standby time isn't going to be as good. On a normal workday, I'm coming home with about 50 percent.
Sent from my Gold iPhone 5S. The "S" is for sexy.