If you don't want to bargain, then Wing Shing is the best since they have fixed price on their items. Their price might not be the lowest but is very close to the market price. Their price applies to both cash and credit card so that is a plus for them.
Leave Wing Shing the last store to visit, you can check the price with the electronic stores around the area first . Fortress,
Broadway and Citicall (some of them now called Suning) are reputable stores. Their price are quite competitive so you can have an idea about how much is the going rate. You can then decide whether you want to buy from Wing Shing.
As for Tin Cheung, I found that they sometimes will quote you a higher price so be careful.
Before going to HK, check the price from this website to get an idea about the current market rate:
http://www.price.com.hk/product.php?p=104946
http://www.price.com.hk/product.php?p=115067
http://www.price.com.hk/product.php?p=102442