For me Anime of the decade has to be A Silent Voice. I've watched it so many times and cried every single time!
Picking a single runner up is tough but probably comes from Madoka Magica, My Hero Academia, MSG Tunderbolt: December Sky, Your Lie in April, Made in Abyss, Scums Wish, From the New World, Promare, Stein's;Gate.
Picking a manga is also tough as several I've read recently which I loved like Blame! and Doubt are pre this decade so I'd probably have to admit that I really enjoyed Magical Girl Apocalypse. It's dark and twisted but also felt original and I never really knew which way the story would go next!