I definitely have an attraction/weakness for natural redheads - but beyond that, hair color isn't a big deal to me. I tend to be slightly LESS attracted to blondes - but not enough to pass over a girl for that reason.
When it comes to hair color, though, I prefer natural looks (even if it's dyed - if it looks like it COULD be natural, that's better). All the pics you posted look relatively natural except maybe the blonde.
If you're going for an artificial look, then it only works for me if you go ALL THE WAY and do bright blue or purple or something like that. I don't care for highlights/frosted look or the "dark hair dyed red/blue" look like the blue anon posted.
Honestly, I'd prefer any shade of brown over red or blonde. I have no idea why, I just always have.
As for the shade, well, I have a slight preference for pail skinned girls, and I don't think black hair goes well with pail skin. So I'd prefer "brunette" or "dark chocolate" in most scenarios. A close second would be "black" hair - the only downside is that it only goes well with tanned girls and I'm not too fond of tanned girls.
Overall: I think "brunette" or "dark chocolate" are the most versatile hair colors, so my vote goes to either of those.
Her's is a mix between black and dark chocolate at the end. That's not my concern though.
I went with B. However, although blonde's always been my least preferred color (besides grey and white), I met this blonde girl last month who blitzed her way to the top of the leaderboard for the hottest, sexiest girl I've ever touched within less than ten minutes of my meeting her. I'm no more bothered about a girl's hair color than I would be about her eye color- it's totally irrelevant in the grand scheme of things. Whatever it is, it'll be pretty if the girl's pretty.