It does depend on the product you are buying. If you are looking for brand names for instance, then you are best to buy from US wholesalers as brand names from China are 99% likely to be fakes. Another exception is liquidation - liquidators in the US will often sell off high quality, brand name products at below cost.
For generic products, China is almost always the way to go. Production costs are very cheap, leaving plenty of room to make a good profit even after shipping is taken into account.