If you consider the charges of the forwarding service, Amazon prices are not cheap anymore. AmiAmi is really reliable, have consistent discounts on new releases (usually 13%, no one pays retail price in Japan), always include every pre-order or first edition bonus, and have a great shipping service even if you are on the cheapest SAL option. I always buy my stuff there. The only drawback is if you want to cancel a order or preorder. There is no option on the website and while they do accept a cancellation from time to time if you do that very frequent you will enter their blacklist (will not be able to pre-order anymore).
Edited: yeah, you have to pre-order early for high demand itens. They can have a few extra units at the release date however, if you do not pre-order elsewhere is worth to check by them.