What are your priorities? The X has optical image stabilization on both lenses so that makes for better low light performance all around than the 8. You will get some shots at night that you might not otherwise get on the 8. Oh and iPhone 8 has only one lens anyway. The X has a very handy 2x zoom that I use quite a bit.
The displays on the X’s are a mixed bag. Some people are having trouble with eye fatigue on the OLED because it uses something called pulse width modulation to turn the pixels off and on faster than your eye is supposed to register. But some people can feel the effects of the flicker in the form of eye strain or worse, a migraine. Even people who have never had a migraine before. I am a migraine sufferer but only get eye strain and it’s not horrible.
Also the displays can come with irregular tints or can change color to a blue tint as you change your viewing angle. This is referred to as “color shifting” or “blue shifting”. My husband’s display does this but mine does not. However, my display has a small pink tint all around the edges of the display. I’m currently trying to decide if I’m bothered enough to try and return it for this reason. At first I was sure I was going to but I’ve since seen worse OLED variations and may just let it slide. OLED is wonderful for looking at photos and videos but this iteration of it is not the optimal display for reading on. I still read ebooks on my 7 Plus, honestly.
Face ID is very good. Just in the last couple of days I’ve had a bit of lag on mine and had to input my code. But each time it fails and you input the code it is supposed to be learning how to identify you from that angle or whatever change it was that caused the failure.
I really enjoy the swiping and do not miss the home button at all. I find it extremely convenient to be able to access the camera and flashlight from the lock screen.
I like the size of the X.
I think the advantages the 8 Plus has over the X include a longer battery life, a very refined LCD display with a good consistent implementation of True Tone (on my X it’s either yellow or salmon pink, yuck) and a more palatable purchase and repair price. The iPhone 8 won’t have the battery advantage. The X falls somewhere between the 8 and the 8 Plus in that respect.
I hope I’ve provided some information as objectively as possible. Good luck with your decision.