Your question was discussed before in an older thread so check those opinions out.
https://talk.macpowerusers.com/t/switching-from-iphone-8-plus-to-xs/9380
I upgraded from an 8 Plus to an XS last year and am pleased I upgraded. I like the smaller size of the XS better (8 Plus was just big enough for me to drop occasionally when holding it one-handed). I also love the convenience of FaceID and don’t miss Touch ID. But the camera upgrades from the 8 didn’t mean so much to me in the year that I’ve used the XS (the 8 already has a pretty great camera).
In terms of speed, I didn’t notice much of a difference but I don’t really tax the processor/GPU in my use of the phones.