Shinjuku GyoenUeno Park(上野恩賜公園) and one is Shinjuku Gyoen(新宿御苑).
I visited these 2 places during the weekend, and got an interesting finding. There were more younger groups (students, friends and colleagues) at Ueno Park and more families and senior people at Shinjuku Gyoen. I am not sure what caused this phenomenon, my guess is alcohol allowed at Ueno Park but Shinjuku Gyoen.
Anyway, I like both locations. Because both places show beautiful sakura and happy atmospheres.