These shows had very similar ensemble casts in similar grades and similar personalities. I'm going to put characters with similar personalities from both shows against each other and you will put in bold which character you prefer.
The main character:
Arthur vs. Arnold
The rich bitch:
Muffy vs. Rhonda
The big bully:
Binky vs. Harold
The smart one:
Brain vs. Phoebe
The female bully:
Molly MacDonald vs. Big Patty
The tomboy bitch:
Francine vs. Helga
The unlucky/picked on kid:
George vs. Eugene
The teacher:
Mr. Ratburn vs. Mr. Simmons
The principal:
Principal Wartz vs. Principal Haney
The main female guardian:
Arthur's Mom vs. Arnold's grandma
The main male guardian:
Arthur's Dad vs. Arnold's grandpa
The best friend to the main character:
Buster vs. Gerald
one is educational television while the other isn't
and wasn't sue ellen a secret bitch?
I haven't seen hey arnold in a long time while arthur is still in syndication
