I'm guessing the 5S will the 4" platform for a while. They might give it a refresh like they did with 5 -> 5C, with battery / radio improvements and maybe some other extras. If they can manage to get an NFC chip into an updated 5S that would be brilliant, especially considering they stand to make more money on the transactions made with those devices, and it's really the main feature that the 5S lacks over the 6/6+.
I've got the 6, and I find it's just a little too big for one-handed use. When I pick up a 5S, it feels so much better, like a true hand-held device.
I never had a problem with the smaller screens (4S was my device before the 6), and I would even spend a lot of time in the web browser on sites without a mobile version. Viewing photos and video are undoubtedly better on the 6, but I tend to take photos / video and then look at them later on my 30" 2560x1600 monitor rather than try to do any editing on the device, even with my 6. And for things like YouTube, I'd rather Chromecast/Airplay them to my plasma TV if they really benefit from a better screen. When I'm on the go, I'd rather have the more portable device.
I'm sticking with the 6, because I don't want to go backwards in hardware, but if they released a new phone that was smaller than the 4.7" 6, and was mostly equivalent hardware other than minor things (e.g. 6+ having OIS that 6 doesn't), then I would opt for the smaller iPhone option. I don't foresee that happening, though.