2nd man would say first.

Because the 1st man sees 1 black and 1 white hat in front of him. So he can't decide which colour is his hat.
2nd person sees a black hat. So he(2nd) will think, if his hat is black, then the first person would have easily known the colour of his own hat as white because there would be 2 black in front of him. But the first person didn't say anything. Which means he(2nd) is wearing a white.
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The second person shall shout first. Reason. The 1 person can't say which hat he has as 2 &3 are having different colours. So his may be black or white. As the 1 person didn't answer for a long time, the 2 person will come to know that he &3 are having different colours. As he can see that 3 has black hat he will be the first one to shout that his hat is white
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