I would say that based on actions, the Nazis are worse (holocaust, WWII, etc)
But based on what each group wants(wanted), the Taliban are worse.
Explanation:
Nazi success requires an initially great amount of bloodshed and misery, but once the "aryans" rule the world, there would be peace.
Taliban success also requires a great amount of bloodshed and misery, though possibly (due to the ability to convert/obey to avoid death) less than the Nazis, except that a world ruled by the taliban's values would subjugate women for as long as they ruled.
A metaphor for comparison:
The Nazis would kill two people. The Taliban would kill one and then make one person (and one of that person's children, etc) a slave, forever.