When searching for a case, the first thing you should know are your PC specs... This will be the largest influence on your final case selection - it will also directly affect your budget (aka cost) decisions as well.
Example:
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You have a monster PC with 2-3 high-end GPUs, a high-end CPU, E-ATX motherboard and tons of storage drives.... well, you're now looking at super towers.... and you probably have a pretty high budget!
Or... you are building an HTPC with a cheap 2/4 core CPU, integrated GPU and 1-2 storage drives... well, you're looking at small-form cases... and your budget is considerably cheaper...
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Next, you're now looking at your noise/cooling requirements. Your environment will dictate some of this (office, bedroom, living room, etc), as will your build (see above). Once again, if you have some crazy setup, cooling will be a priority - but if not, perhaps you don't really need more than a few fans...
Last, look at aesthetics: even after narrowing down your choices, there are still tons of cases to choose from - pick the one you think looks best. Even the pickiest PC owner can probably find something that appeals to them, and, if not well.... there's always custom case modding
