An HTPC has to be especially quiet so as not to distract from the media it's playing. With this in mind, we tested these cases to see how much noise they put out.
To get these results, we put a fan-less PSU in each case and attached all of the cases’ fans, then took a decibel reading 4" from the top front of the case. Remember, because we used a completely silent PSU to drive the fans, the actual noise output when using these cases with a typical PSU and fan will likely be a bit higher. Using the fan-less PSU did let us eliminate other noise factors and focus on what the cases put out.
While it would be simple to declare victory for the quietest case, the noise benchmark reflects the unequal number of fans these cases have--the Moneual 972 is the quietest with two fans; the Thermaltake DH102 is in the middle of the pack with three fans; and the SilverStone CW03 is the loudest with four fans.
You can always detach a fan to make things quieter, but it's considerably more hassle to add fans later, especially in HTPC cases where there isn't a lot of expansion space.
In any case, the Thermaltake DH102 appeals to us in the stock configuration because of its reasonable noise paired with a large 120 mm intake fan and two 60 mm exhaust fans, which should provide decent airflow.