Same here, I could live with the 6 fine but every time I went back to the 5s, it felt so much more comfortable. Since it's harder to sell the 5s because of so many cheap prices out there, I decided to sell the 6 and stay with 5s for now.
I miss the big screen a bit for some things, but I don't really miss the 6 much.
The 5s is a beast in speed, and the camera is better than the 6 (no paint-like artifacts)
I think my biggest issue with 6 is that 4.7" isn't large enough to justify the upgrade, I really wish it were 5" or 5.1" like the Galaxy, then sacrificing one-handed use for a bigger screen would make more sense.