The consensus has it that the big winner of the Iraq War was Iran, in that the toppling of the Saddam Hussein regime removed the major barrier containing Iran's regional ambitions. Certainly the Shiite-dominated and Iran-friendly government in Baghdad has freed up Tehran's hand across the region -- even if, as I've argued before, the inherently volatile nature of Iraqi politics means that Iran has inherited some time- and energy-consuming responsibilities in Iraq along with its increased influence. But I'd argue that the fears among Middle Eastern Arab states of Iran's growing regional reach have more to do with their own domestic politics, often with regard to Shiite minorities, than with the strength of Iran's influence, the gravitational pull of its industry, or the attractiveness of its governance model.
The same can't be said for Turkey, which has also benefitted from the dramatic changes in the region's geostrategic landscape wrought by the Iraq War. This N.Y. Times article detailing Turkey's enormous and growing trade ties in the Kurdish north, as well as its political influence in Baghdad, is only part of the story. Ankara's opposition to the war, and the Bush administration's obstinacy in pursuing it, in some ways prepared the way for Turkey's rebalancing of its foreign policy approach from a Western-focused alignment to a Turkey-centric strategic hub. And the power vacuum created by the fall of Saddam Hussein, though initially as destabilizing as Ankara had feared and warned, subsequently helped create the space for Turkey to assume the regional role it aspired to.
But in contrast to Iran, it has done so on the basis of an economic boom unfettered by mistrust, isolation and, most importantly, international sanctions. And it has done so while embodying a model of democratic governance that is infinitely more palatable to its international partners, both existing and potential, beyond the region -- and ultimately more threatening to the authoritarian autocracies within the region than that of Iran.