Iran is more of a threat. It is a bigger promoter of militant Islam, it has the largest military force in the mid-East except for Israel, and possibly Egypt. It is building up that force extremely quickly. It is subject to internal turmoil which drives countries to wage war. It has weapons of mass destruction, including a well established nuclear program.
Having said that, Iraq should be attacked first. It is the logical first dominoe to fall, and makes for the best staging area for further operations into Iran, or Saudi Arabia. (and don't think for a second those options are not being reserved by the administration)
Oh, I disagree, the government of Iran is losing power with its citizens. Their chief cleric resigned out of protest to Iran's human rights record.
Agreed. Besides, Iran is already pretty close to tipping anyway, because the mullahs are in trouble. An overthrow of a regime next door should be the final push needed to produce a pro-western Iran.