This is a very good question!

If you look up 铜臭 in a dictionary, the pronunciation is tong2xiu4. However, nowadays people always say tong2chou4， tong2xiu4 only happens when you are taking a Mandarin exam and they will not give you your points if you dont read it that way. :)

So, if you are talking with a Chinese person, better to use tong2chou4. If you are taking an exam, please use tong2xiu4.

gail@popupchinese.com