If the person who's going to be using the phone is careless and drops the phone often or perhaps has children in the house then look no further than Nokia. It's built like a tank!
The phone is tougher than The Nokia 3310!
Samsung J6 is purely made of squeaky plastic, has 'much' lower specs than the other phones you've listed here and its only saving grace is the OLED display.
As for Mi S2, it's pure garbage, period. Best to go for Redmi Note 5 a.k.a Note 5 Pro, Redmi 5 Plus, Mi A1 (Which I personally own) or perhaps The Mi A2 Lite (Notched display, ugly).
Hope it helps.