This is tricky because I think there is also very much an age factor to it. Black can be hard to wear when you get older. Brown, IMO, is a much softer and forgiving neutral.
Then there is also the contrast issue Imogen talks about on her site - if you have black or dark hair, black looks great because of the contrast. But if you are blonde with light eyes and fair skin, black can look jarring.
I have both brown and black in my wardrobe. But, I am thinking that grey is actually the best neutral for me all around. It's a cool color and I look best in cool colors. And it's lower contrast and softer and more forgiving now that I'm in my 40s. I feel like grey tops brighten up my face and make it glow, whereas black tops have a way of making me look tired and my skin looks dull.
In fact, I have photos of me as a child, when my hair was super light blonde, wearing black to dress up as a witch for halloween, and even though I was only 11 years old, I think I look OLD and horrible and haggard. LOL. And often if I wear a black dress, I feel this effect very acutely - I feel like a witch! A brown dress, much better.
Brown tops, I look less tired - and it brings out the green in my eyes. But it's still not ideal. With either brown or black tops, I need a necklace that adds color or brightness near my face.
But - brown isn't so bad. Especially if a dose of white is added to it. Brown slacks or skirts can go with a lot of sumptious, rich, softer colors too, so that is a plus for it as a neutral.
I'm rambling now (because I'm trying to figure this all out for myself too!) .... but I think another factor is jewelry: which looks better on you, gold or silver? If you say silver, then black is a better neutral than brown. If you say gold, then brown is a better neutral than black.
I definetly look best in silver jewelry, and I probably wear silver about 90% of the time. But I don't think I look too horrible in gold either.
There's also the factor of my dye job. If my hairdresser goes with low-lights and brings out the natural red that's in my hair, then browns and gold jewelry look better, hand's down. But if my hairdresser goes with highlights and amps it up (like my hair is currently) then black, grey, silver.
My hairdresser tells me that there are three types of blonde highlights: ashy blonde, golden blonde, and neutral blonde. I definetly look best in neutral blonde highlights. Ashy highlights look absolutely horrible on me, and so do golden blonde highlights. So this tells me that I can possibly go either with browns or blacks. Does that make sense?
Whereas I think Angie is more of an ashy blonde (near-white blondes are), so it makes sense to me that she would look horrible in brown and great in black.