Who poses the bigger threat? Islamic State or the Islamic Republic of Iran? It's actually a false dilemma. Both the Sunni and Shia side are equally hostile to Western values and to Liberty at large. But some are working hard to get the West into the Sunni camp.
Islamic State vs. Iran: Which Threat Is Bigger?
UPDATE: Speaking at the U.N. General Assembly, Israeli Prime Minister Benjamin Netanyahu made the point that if Iran is armed with a nuclear bomb, it would pose the "gravest threat to us all". He added that defeating the Islamic State of Iraq and Syria and leaving the Islamic Republic on the side is akin to “winning the battle and losing the war.” (Source) Both sides, battling it out in Iraq and Syria for Shia or Sunni hegemony in the Middle East, are in fact equally evil and hostile to Liberty.