Mighty Mouse was my favorite. The music in the Terrytoons Mighty Mouse stood out. I seem to remember the mouse leads had operatic voices. Animation, compared to Hanna-Barbara/Filmation made for TV stuff, was very , very good.
I am partial to the early B&W Fleischer Popeye cartoons. I think one of them still holds the crown for "most violent" mainstream cartoon of all time.
3:00 minute clip