First of is what I am not going to tell you:
where to get it,
how to get it,
how much will you get of it,
exactly what you get when you donate.
The unknown variables at this time are:
does a corrupted squad receive a corrupted item and an/or redeeming item,
does the level of the squad affect the level of the item,
do the traits of the squad affect the items characteristics you get.
Known variables [ SPOILER - DO NOT READ ON IF YOU WANT TO TEST]
Every squad will receive exactly the same item - per that squad, no matter how many times it donates it ( confirmed trough multiple reloads ),
the item will have the same characteristics per squad every time you donate, so you need to donate it only once to receive the item,
to test out what each squad will receive., you need to go trough all the squads once, save take pictures and reload,
then go trough the screenshots, and decide what you need to give to whom.
To address the cheating factor, there is little to no cheating in this action IMO, if you know how it works.
To know how it works you need to read this ( or test out for yourself ), and were warned that it might spoil your game, added also is that there are unknown variables that might apply if your mileage varies ( aka different level, traits, corruption ).
If we are talking about one item you can get, I will tell you that FC, Avitus and Jonah, receive exactly the same type of one item with the same characteristics ( no matter the level, or traits ) and added stuff, but that item is personalized per each squad that made the donation, and no other squad can use it.
Personally, I passed best with one squad, and that is the one and only item I will show you, so again SPOILER if you do not want to see it, do not
click the link: