I think it would depend on how/why it was said. For example, if a woman said "Wow, you REALLY need to do ______ with your hair . . . it looks horrible!" then it may be seen as controlling However, if a woman said to a man (generally speaking), "You should cut those bangs so I could see your beautiful eyes!", then I think it would be sweet and more of a compliment/conversation starter
I think even flattery can be controlling, if the end goal was only to get him to cut his bangs.
I think I love you no matter your hairstyle would be more appropriate.