Quietness most depends on your cooling and PSU now. Most cases these days, high end and cheap all have tons of 120mm fan vents and vents around the drives, and all along the front of the case.
No matter which case you go with, make sure you get a very quiet aftermarket CPU cooler, pick video cards with low fan noise and check reviews for most quiet power supply for your build. And if you are going to build a PC for home theater, you can simply underclock your CPU and go with passive cooling and have no fans at all and will have 0 noise then.
I personally think most newer cases are more noisy since they have so many vents. The power button became stuck on one of my old systems. I bought a Cooler Master Elite 360 case (which is silent with my Core 2 e7500 system) and used it to replace the broken case of my Pentium 4 670 3.8Ghz space heater.
The old case for the P4 was quiet. It only had one mount for a 80mm fan and I only heard the PSU fan. But after installing the system in this fully open case, it sounds like a vacuum cleaner because you can hear the CPU fan clearly with all the vents.
However, the old case the CPU was 65 degrees C, the Cooler Master is only 52 C.
The same Case with a P43 board and a Core 2 Duo e7500 is silent. PSU and video card is same on both systems (9800gt). BTW, the Core 2 in the same case is 34 C.
PSU was same and video card same in both cases... so don't worry about the case as much as the fans on the CPU, PSU and GPU.