Attack on Titan - Beautiful artwork, great story, amazing plot, etc. - Action
Full Metal Alchemist: Brotherhood - Great story, characters, art, etc. - Action
Clannad: Afterstory - Made me cry like a six year old girl. Thought that everyone saying that it brought them to tears was just exaggerating... but I was sadly mistaken

- Slice of Life/Romance
It's hard to say what is the best because people's tastes vary so much. For me, I would probably say After Story but I know plenty of people who hate that kind of stuff and would undoubtedly pick FMAB or AOT or Code Geass or something