That's not the easiest thing to quantify, with neither unit being completely immune from issues. It is worth pointing out that the Citroen uses a more conventional torque converter style automatic, and one built by ZF Group, which is widely used across the car industry and well proven at this point. The Hyundai does have a much better warranty, though, lasting for five years and unlimited mileage, compared to Citroen's three-year, 60,000 mile warranty, so you'll be better covered with the former in the unlikely event of a transmission issue.