Favorite Feature: Mine, which I'm mainly citing because I haven't seen mentioned, is how smoothly the screen responds when you swipe up for the home screen. It's an incredibly fluid and natural gesture. I suspect this is achieved with the higher 120hz-touch-sampling-rate that is unique to the iPhone X.
Least Favorite: Reaching for the upper right corner to get to the Control Panel. I hope Apple comes up with an alternative method eventually, since it could be added easily in an iOS update.
Honorable Mention for Favorite Feature goes to FaceID. It performs near flawlessly for me, such that it seems almost magical. I particularly find it beneficial when opening a locked app, where the scan begins as soon as I tap on the app icon and I'm let in immediately. I do find FaceID a bit more cumbersome when using ApplePay, but I think it will improve with time as I become more accustom to it and/or Apple smooths the process.