I was considering the same exact thing due to me being on the love/hate ride of the 6+ and I really loved my iPhone 5 size since it was small and handy to put in my pocket without noticing, but was able to do so much and so conveniently whenever I needed it to. The 6+ is amazing to use it, but it's not the same kind of experience and doesn't feel like my handy little gadget anymore.
No experience with the 6 personally, but the main thing drawing me to the 5S over the 6 was the substancial price difference between the two.
No experience with the 6 personally, but the main thing drawing me to the 5S over the 6 was the substancial price difference between the two.