I think his hair is getting progressively worse as the films go on, except for maybe the first movie. I didn't like how, when he woke up in X1 and started running around, his hair just flopped down like a normal hairstyle, as if the gel in his hair had come out. It made it as if he deliberately styled it that way when he's normally awake, but hadn't had a chance to at that point.
I liked his hair best in X2 or X3. All the other films have been rather bad and not distinctively Wolverine enough. What the heck is that style in Origins?
Not a fan of his look in FC or The Wolverine either. Was it a wig in the original trilogy or did he use his real hair? Is he losing his hair now or maybe it's not thick enough to do that anymore? But if so, why not use a wig?