Blonde > Brunette > Redhead for me I guess, but it's a mild preference at best (so mild it was actually kind of hard to decide which>which) and never an important factor on it's own, I've seen girls with all 3 hair colours that are really attractive.
Some things that go with it though make it slightly more important as a preference. F. ex. blondes can have some short body hair and it's neither off-putting nor very visible. Redheads are usually spotty and pale, which usually bothers me a bit, though it really depends girl to girl, some look fantastic (although in general I preferred dyed red). Brunettes not shaving regularly can bother me to a point and they sometimes have very pronounced brows, which I'm not exactly a fan of.