Get the phone that will be supported for at least the next 2 years.
Will Lumia get Windows Phone 10?
Will S4 / G2 get Android 5 / 6?
Will 5C get iOS 9?
Battery life is about the same on most phones, and there are power saving settings for all. Reducing brightness, turning off sensors, gps, WiFi, Bluetooth increase battery life, limit the amount of background apps etc.