The main difference between these phones are the size so it depends on what you do with it. If all you do is the simple things like texts and calls then the 5 wins as both can do it very well. If you want to surf the web for a long time, the 6 is better unless you have good eyesight. This is the same for videos and games. Also the 6 has the advantage in the camera.
So really it depends on what you do with it. 5 for one hand usabilty or 6 for a multimedia experiance. The choiice is yours.