I used my cousins 5S a bit whilst on holiday and must say it felt a lot nicer to hold and actually faster for general use than my IP6 (menu, phone, messages etc) The display also looks sharper. Yes, the screen is quite a bit smaller but the size to me just feels more like a phone.
The only downsides to me are audio quality, the 5S sounds quite a lot worse that the IP6 for playing music, battery life and 32GB size instead of 64GB. The latter I could live with but listening to music is one of the main things I use it for.
Anyone gone from an iPhone 6 back to a 5S?