I recommend S4.
for better battery performance, do not let your phone overheat. overheating is mostly when you use phone while charging or when you use thick silicon type cases. Li-ion battery gets swollen and weak from overheating.
samsung plastic body is not very good for heatsink, especially for multi cores.
i see many people using home button to close spps. it actually minimizes the apps, hence draining the battery.
battery draining not so useful features like GPS, Bluetooth, sync etc should only be used when necessary. people keep them turned on, even when they are not using them.
the S4 that i bought new had battery backup of 24 hours, easily without root. it got overheated (45C +) multiple times and battery got slightly swollen, then 6 hours max battery time.
