Lena x Shin hits even harder because they never see each other until the very final episode. Witch from Mercury is on my watchlist so I'll have to give it a go.
I absolutely love Boku no kokoro yabai yatsu. Currently this has to be my favorite romcom. It starts weird but it gets so sweet by the end of season 1 you're going to get diabetes.
Another great show I can recommend is Golden Time. It's like Toradora but with older cast. I have to admit I enjoyed it way more than Toradora. Maybe because it was exactly my type of humor or because some situations were very realistic. Whole show is not like typical rom-com. It feels like it could happen for real.
It was the second anime I watched. Funny enough it's been so long I barely remember a thing about it. I don't even remember if it was good. Maybe I should rewatch it...
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.
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.
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.