Bebop is my favorite series, followed by Helsing. But if we're talking best ever stand alone. Ghost in the Shell was GOOD! Akira was BETTER! But, the standard going for almost 30 years now is VAMPIRE HUNTER D!
Considering I JUST WOKE UP, I'll post a summary of someone else's review.
The break down is it's the story of the struggle between two empires and the two heroes at the center of it all, each fighting for their own reasons. On the Empire side there is Reinhard Von Lohengram, military ace and nexus point to bring about change within the Empire and do away with the corrupt nobles. On the side of the Free Planets there's Yang Wen-Li, who joined the military just to pay his tuition to be a historian. This makes him well versed in past military tactics and a genius in his own rights. Yang to wishes an end to the corruption in the so called democracy of his government.
The differences are the two characters approach, Lohengram wants more power to effect that change and Yang wants none. If you look at these two characters they want the same thing for their people, you think they could have been friends if the situations were different.
The series is epic in scope and legendary in it's execution. Making it one of the best anime series that hardly any one has ever seen.