Both hats were brought out for the same month and sold for the same amount, so technically they are equal in terms rarity. However, the Princess Minnie Hat has reached a greater popularity than the Green Backwards Hat. Though, due to the fact that there are rumors that the Princess Minnie Hat will be coming out later this year, its value may have dropped in some trader's eyes. While the Princess Minnie Hat may be worth more (the demand is greater than that of the Green Backwards Hat), the Green Backwards Hat is still in high demand as well. Therefore, since the offer included other rare items, it should be a pretty good offer. If you post their offer, many people can tell you what they think.