What's the best way to charge my IPhone 5S?

Is it best to turn my IPhone 5S off or keep it on while charging over night?

Phones always charge faster when they are turned off, but the difference isn't necessarily very big.

It doesn't matter to be honest.

If you charge it overnight for quite a few hours it will be on charge when its already full, therefore ruining the battery better off charging it during the day