If there's nothing in the comparison in https://www.gsmarena.com/compare.php3?idPhone1=9738&idPhone2=9646 that makes one of them clearly better for you than the other, both will be good amd none of the two will be bad.
You can either throw a dice (1,2,3 = Xiaomi, 4,5,6 = Galaxy) or buy the cheapest of the two (why pay more than needed?).
I am using Galaxy S7 Edge from past 3 years and i am quite satisfied with it no complaints. But now it is old not getting any updates and battery are dying. I thought it is time to change the device rather changing the battery. So in my budget i am considering only two devices after a lot of researching, Xiaomi Mi 9T and Galaxy A70. I find both of these Head to Head specs wise, cameras are almost same displays are almost same but Samsung A70 has slightly lower Pixel Density. I minimum use my device for one year maybe two but not thinking about changing my new device for minimum one year. So please help me decide which one will be good for me.