Personally, I think Guangzhou is better for garment wholesale business, which is mainly concentrated around Guangzhou Railway Station. I recommend you to have a look at Dongguan and Humen which are importance farment factory bases. Shanghai Qifu Rd is also a large and well-known garment market gathering some stuff from Hangzhou and South Korean. If you have time, you can visit both of them, well, although the expense on the transportation between them is a little high.