Walk up to a bloke, any bloke. Ask him what kind of hair he prefers on his girls. (on their head, for those with a crude bent ;-). I suspect most people would say long hair, and colourwise, a definite leaning towards blonde.
But I prefer dark. At least for most people. There are occasions when lighter blonde hair looks absolutely gorgeous - mainly on models when they're gorgeous anyway (case in point: Dannii Minogue in the "All I Wanna Do" era, Pamela Anderson sometimes); but brunettes definitely get my vote. Dark blonde works too, or rather not "peroxide" blonde.
But look at the other side (just as examples you'll know (most) of): Kelly Brook, Courteney Cox, Emily Booth, Jayne Middlemiss, Dannii in current form or early 90s "Love and Kisses" (gorgeous), Katie Holmes, Teri Hatcher (earlier superman series before it went short), CZJ). Then there's the fraction-second snatches of Britney (Spears) in the "Toxic" video with long v.dark hair... (ok ok, enough)