Another consideration is noise. After all it can be hard to focus on whatever you are working on at your computer if it is screaming like a banshee. As shakran mentioned, more fans = more noise. Preferably a case with a 120 mm fan would be best. Plus a power supply with only one fan helps. Plus good heatsinks on the processor and video card. Using a huge heatsink with heatpipes and tons of fins with lots of surface area dissipates heat more effectively than a smaller heatsink with less surface area and no heatpipes. As a result you get more cooling from the same fan or can even use a slower spinning fan to reduce the noise level.
I have an old Antec SX835II case, an older Core 2 Duo processor, and an old AGP card with a passive heatsink. With the original Antec power supply, all 5 case fan spots filled, and the stock processor heatsink and fan and no fan on the video card the computer was loud. And hot. Processor temps typically around 130 degrees F and the video card would reach an eye popping 175 degrees F just doing desktop apps. I recently made some changes, while keeping the same case for the time being I replaced the power supply with
this one, put in
this cpu cooler, and promptly replaced the fan on the cooler with
this one. I also figured out how to mount this
92 mm case fan to my passive video card heatsink. I got rid of all the case fans, and mounted the cpu cooler so the fan points right at the holes left from the 2 rear case fans. I left all 5 case fan spots open, and the result is I went from 8 fans to 3 total. And yet my cpu temps dropped about 20 degrees and my video temp dropped about 65 degrees, just due to the more intelligent layout of the fans and the more efficient processor heatsink. Plus the fans are quiet enough I don't hear them, just a little noise from the hard drive.
When I built my first computer I never took noise into consideration, and now having done so it makes using the computer so much more pleasant.