Certainly Queen Elizabeth II. While Bart Simpson is a popular cartoon character, (a) he is not real, and (b) not everyone watches The Simpsons. In fact, in many countries, they have never heard of that program. But the queen is not only a real person; more importantly, she is a symbol of a powerful nation (England), and as such, she is far more famous all over the world.
Seeing as both are widely known figures, I would have to say that Queen Elizabeth II is more popular since her existence has been longer.
Older people-the Queen, younger people-Bart. Worldwide-Bart (IMO)
Bart Simpson
Probably Bart Simpson !
Bart Simpson
Bart Simpson
Bart Simpson
Bart Simpson
Bart Simpson
Bart Simpson
Bart Simpson
bart simpson
Obviously Bart Simpson