macmall.com is better because no sales tax for many states

Amazon started collecting sales tax in many states. My state(CA) has near 9% tax. That's just too high to ignore. 
like today's Sony NEX-3N $349 at Fry's is a good deal. However, it will around $390 after sales tax, which makes the deal not that hot because previous lowest was $400 from adorama.com. 

For Apple products. 
macmail.com often has good deals on Apple products. no sales tax to many states
bhphotovideo.com has no sales tax other than NY. 
newegg.com has no sales tax other than CA. 
buydig.com has no sales tax other than NJ
adorama.com also has no sales tax in many states

Price in these online stores are very competitive, often have more discount than Amazon.