It’s clear in the video(YouTube link), that one-handed usage of the new 4.7″ handset won’t be as comfortable as with the iPhone 5s. This can be expected, and is an unpleasant side effect of large phone screens, coupled with the now-mandatory Touch ID fingerprint sensor at the very bottom. This prevents Apple from using a smaller bezel there, although the top one is pretty large, too.
Decreased overall ergonomics aside, the iPhone 6 might still be fairly comfortable to operate with one hand, thanks to the very thin side bezels, and elongated shape of the handset. As you can see in the direct comparison with the iPhone 5s display panel, the FaceTime camera has been moved to the left of the earpiece slit, instead of being placed top and center, which might throw off your video chats at first, until you get used to the new position.