Who had been in your opinion the worst Pope of all so far?

In my own views, the worst is probably Pius IX or X

IX because it was under his pontificate that the First Council of Vatican published that horror, the dogma of Papal Infallibility...

X because he was a complete reactionary retrograde who did much to ensure the Church's decline by divorcing it from the concerns of the faithful and making it go away from the real world.

As for those who say Pius XII... I'll tell them that there's not much he could have done since lack of respect to Hitler or other fascists might simply have meant that blackshirts (or even German troops, remember how the Germans took Mussolini 'under protection' in 43 or 44?) could have raided the Vatican and removed the pope and any dissenters... Of course, his doctrinal (and "infallible' rantings about Marial dogma (namely the assumption) still make him a complete crank and not a good pope at all.

Pope Paul VI

Alexander the VI. The one with the bloodthirsty son and a poisoning ***** of a daughter(Borgias). You know with the orgies and the naked boys... And he liked the Belgians. (Okay not that, but still...)

Pius XII, he turned a blind eye to neighboring peoples suffering & should NOT be beatified.