Well... I think it depends on the guy! Lots of people commenting on this have said how their curly hair makes them look younger or whatever... and personally, I agree. But that's not the case with everybody
Don't just straighten your hair because you think guys will like it better. If you're gonna straighten it, do it for yourself! Do it because YOU want to change your style for a bit, not for anybody else. At the end of the day, it's YOUR hair, and if you straighten it all the time, you're gonna damage it. Trust me, I would know. I used to straighten my hair all the time for one year. I never wore my hair in its natural state, because I thought that my curly hair made me look like a child, and I wanted long, shiny straight hair. What I got was dry, damaged haystack hair. Well, since then I've discovered that there's nothing more beautiful than a healthy head of hair