Trans fats act like saturated fat by increasing "lousy" LDL cholesterol but it also decreases the "healthy" HDL cholesterol. So, we know that trans fats are worse than saturated fats, but how much worse? Two times. Trans fats increase the total cholesterol to HDL cholesterol ratio (a higher cholesterol to HDL ratio is bad) nearly two times more than saturated fats. Avoid them!
Source: Ascherio, A, Willett, WC. Health effects of trans fatty acids. Am J Clin Nutr. 66 (4 suppl). Oct 1997.