Bounty hunters, get them to gear 11 and that's it, they will have served their purpose of givin you Han's falcon, chewy, and can do both galactic bounty event at gear 11, also imperial troopers perform better on the rebel round up and can also do the forest moon assault battle.
Scroundles, at this point they are completely useless and don't have an assault battle.
Ewoks, just get them to gear 11 to get c3po and don't touch them again.
Rogue one, only get them to gear 11 if you are still doing hoth TB, their ships don't need high gear to be useful.
Smugglers, again complete joke faction, just get chewy and Han to gear 12 or higher to do the especial mission that they have.