I switched form the iPhone 5S to the Samsung S5 in April.
The S5 battery life is very good. It buries the 5S, and in a pinch, the power saving mode got me through another 4 hours on a measly 7% battery life.
I don't know what iPhone 6 has to offer, but this whole form over function routine is concerning. I don't need a thinner phone as much as I need a longer lasting phone.