Depends on brand, but I would say from what I've notice, that the Gamma and Seaguar regular fluor carbon is stiffer. This doesn't equate to a better line though. You want to check the abrasion resistance of the line as well. Some of those fluoro lines can't stand a scratch. The real question is: fluoro or mono....do you really think you are going to find a fish that will break 40 lb or 50 lb test line? Your not would come undone before you could break the line unless you are doing something stupid like using the same leader all season long or using a 40 lb leader for halibut. If you're only looking at stiffness, then go the store and feel the lines. Depends on brand. If you want to catch fish, look at the hole picture. Resistance to abrasion, UV resistance, overall line life, stiffness, color are all things you should consider. Tup: