I believe the best starter animes must meet some criteria:
not too long (seeing something having hundreds of episodes is a huge hurdle)
self-contained (no spin-offs of other franchises that you need to know)
completed (no “if you want to know how it ends you have to read the source material or hope for a second season”)
no need to know cultural references (what the fuck is a shikigami?!)
universal themes (love, hate, friendship, hardship, etc… Stuff that applies to everyone)
characters should be likable (no one keeps watching if they dislike the characters)
interesting from the start (no “uh, it gets great from the 5th episode, just keep at it”)
interesting throughout (show shouldn’t fizzle out or run out of steam)
normal visuals (yes, shows with unique art styles can feel fresh for someone with more than 1000 shows under their belt, but for a new watcher better keep it normal)
not mundane but not too far “out there” (just the right amount of fantastical)
no off putting material (gore, over-the-top violence, etc.)
it should end on a positive note (I wouldn’t have touched another anime ever again if Grave of the Fireflies were my first one)
I believe the best starter animes must meet some criteria:
With all those criteria listed, I believe the best show that ticks all the checkmarks is Anohana: The Flower We Saw That Day.
Great pick