I would say Shiinotic and Mimikyu. Their primary typings will help cover types not covered by the pokemon already selected or will provide more coverage. My only thing is Shiinotic has a low base stat which may hinder it on your team, but it never hurts to have a grass type.
Yeah this gen really makes it hard to decide last time i got a hard time deciding for my team was gen v really frustrating since i really wanna try this 8 pokemon but I dont want to do shifting cause i never really done that ugh!!!