Local stores, or manufactures' own retail sites, for me. Been burned too many times by Amazon for them to ever regain my trust.

I'm in Austria. There are price aggregator sites likes Geizhals and Idealo that helps you find deals across many stores. More often I just go to a store I know and like. It happens I pay a little more, but not having 15 cheap options with one off brand names is actually more a pro than a con..