Using both phones, both are great.
Camera is better in mate 10 lite, display has more brightness and is bezel less, battery lasts a few hours longer, software has more features like face unlock, ar lens, dual apps etc
Mi a1 has slightly smoother interface, ir blaster, usb type C and android oreo.
Android oreo is also coming on m10 lite with treble so we should start seeing custom roms on that phone as well.
You can decide which of these features you want more and go with the one you think you will enjoy. Both are great. I'd go with the Mate 10 lite.