In my opinion the Holy Grail of medicall shampoos for very bad breakouts is: Kertyol by Ducray, this was prescribed by a dermatologist when I had an extremely horrible breakout of SD (my head was full of wounds and dry flakes, and my hair was falling in patches from the worst affected areas).
I used this one http://aptekaslonik.pl/images/prod/6154/ducray-kertyol-szampon-125.jpg
It worked like magic, so from a head full of scales and wounds, to an extremely happy clear skin that felt great, my hair had a nice herbal smell and the overall feeling was amazing. After few weeks the skin normalized so I was able to switch back to a normal Zink Pirithione shampoo for maintenance (head and shoulders or Syoss).
I would have liked to continue with Kertyol but it was too expensive for me for long term use.
Warning: There are many types of Ducray products for different types of SD or for Psoriazis, so it is good if a doctor is familiar with it and will prescribe it according to your condition. Or do your research first http://www.ducray.com/en-gb/hair-care
Selenium Sulfide Shampoos are also effective for me, but it took a long time to become effective_ 2-3 weeks until clearing up 100% of the dandruff.
Zink pirithione shampoos as Syoss or Head and Shoulders are effective from first uses but only for long term maintenance, not for treating a breakout. If you have a horrible breakout, these might not cut it, you might need a strong medical one like Kertyol for a while.
Nizoral is one of the worst ones, don’t try it, waste of money. It clears the skin but the skin does not feel good afterwards, Also it is only working for a very short amount of time, and then the problem is back in full force. My doctor said that he would not recommend it because it looses effectiveness very quickly and patients usually don’t like it.