I can't say the best but these are what came to mind first.
Love, Chunibyo & Other Delusions. A slice of life story about a few different pairings getting together. But mostly about a pair becoming more mature and dealing with trauma.
Chobits, a robot falls in love with a man, exploring the ethical and social issues with that.
Insomniacs After School is an unique pick. I also enjoyed it a lot.
But for me it is Toradora! or The Danger in my Heart. Both for different reasons.
And an unique one for me would be Love, Chunibyo & Other Delusions.
Your name (Kimi no Na wa).
I've watched it three times now and every time I feel like a 12yo kid again. Waking up to life and falling through the depths of all possible emotions.