Best interest
You have good intentions for something or someone
You like me but your dating someone else I’ll keep it in your best interest 😉
best interests
The term for the most blunt and honest type of suggestion given to someone in a time of strife.
US Coast Guard admiral Richard Larrabee said after finding pieces of wreckage from EgyptAir Flight 990 "We believe at this point it is in everyones best interests to no longer expect we will find survivors in this case".
CHILDS BEST INTERESTS
A current or future physical , emotional enviroment for a child suggested by state (family services) only with the consent of the childs parents & grandparents except where there has been a criminal conviction for abuse against said child
it`s in the childs best interests to remain in care as there may be a risk of emotional harm in the future