6 for sure, 5s is a way somewhat small for mobile nowaday i mean the size doesn't sastify me at all, 6 has bigger screen and its a completely different feeling when i use it to watch film in comparison with 5s
I would definitely prefer iphone 6 rather than 5, 6 is greater than 5 and plus it has new features. Also, the size of the phone is really important for me like I can do all the things i need to do if I have big screen size.
Both,it depends on your particular use case.If you need a phone to operate with one hand go with iphone5 and if you don't mind to operate your smartphone with both hands iPhone 6 should be your choice.