This may sound superficial, but hey, it actually is a about a superficial matter, so I'm fine with it. ;-)
I really like natural redheads.
Actually, I dated quite a lot of them compared to their "rareness".
But I love those really bright red dyed girls.
It makes a hot woman them even hotter(not all, but most of them).
I am fully aware it isn't a natural hair colour, but I simply can't resist them.
...well as long as they look good. As mentioned by others before, women who are not nice to look at, don't look appealing no matter what their hair color is(while a different hairstyle seems to do miracles in some cases).
Oh and about men with red hair I don't have any specific opinion.
Some are nice others assholes.
The usual.