I've had the 8+ and now the X
iPhone 8+
1. Bigger content (images and video due to the extra width). If you use your phones in landscape a lot then the plus is great option.
2. Battery Lasts longer (see below)
3. Can be awkward to hold one handed, not as stable as there are times you need to balance it rather than grip it. Reachability works great though.
4. Finger print recognition. Easier to unlock the phone if it's a distance away from you.
5. Great build quality. The SG I had just looked great.
6. The screen is very good. True tone is really nice and after you are used to it, all other displays look blue in comparison.
iPhone X
1. Slightly smaller content but you do get more text on the screen without scrolling. I had the two side by side for a while and there is no getting round it, the plus does allow images and video to be bigger compared to the X but, the screen of the X is very very nice. Colours etc are fantastic.
2. On normal use, the 8+ had about 65% battery for me at the end of the day. That's with 4-5 use and 15hrs standby. The X is giving leaving me with about 50-55% battery. More than enough. Of course, YMMV depending on what you use it for. That said, you'll comfortably get a full day + and I always charge at the end of the day.
3. A lot easier to hold/grip and with reachability switched on, is also easier enough to reach the top and trigger the Control Panel one handed. Fits the pocket better as well.
4. Face I.D. I was sceptical about this beforehand but, I'll stand corrected... it does work really well and I haven't really missed the Finger scanner like I thought I would. In fact, it makes reading and deleting emails from the lock screen easier.
5. Again, as with the 8+, terrific build quality. The silver feels and looks incredible.
6. The Screen is really good. In fact, you only really appreciate how good after using it for a while. The colours are great and look painted on the top. You feel really close to the image. I have also grown to like the notch... odd I know!
7. Don't mind the gestures... doesn't take long to lose the muscle memory from the home button phones.
Both are fantastic phones so don't believe the "iPhone X is way better than the rest". They're just different! They're both top end phones that handle differently.
In the end, I like the smaller profile with as near as dam it the same size screen as the Plus. I use my phone in portrait mode most so, the X really does work out better. Easier to grip etc without feeling like you may drop it.