Depends what your expectations are.
A few things to take into consideration are:
Bearing type
Sleeve bearing -cheap, noisy and gets more noisy very quickly as it ages and the lubricant dries out. Not recommended for horizonal use.
Rifle bearing- same deal as sleeve except that the spiral grooves (rifling) on the bearing surface allow the lube to be pumped over the whole bearing surface so it can be mounted horizontally.
Ball bearing- Better than sleeve/rifle. Expect to pay a bit more than the these also. relatively quiet for most of it's lifetime but can age prematurely (as do sleeve/rifle) with excessive dust buildup.
Fluid (sometimes marketed as Fluid Dynamic or Enter) bearing- sealed bearing-pretty much silent, long service life, fairly expensive.
Magnetic bearing uses two magnets repelling each other instead of a physical contact area within the bearing. The only noise is that of air flowing over the fan blades. very long service life.
In addition any of these fans can have PWM (pulse width modulation) -variable speed control that can be altered automatically via software. Characterised by having a four-pin connection -either fan header, or molex.
The most important value tends to be the actual volume of air a particular fan can move (how much pressure it generates) since a lot of fans will state a number in cfm (cubic feet/min) or m³/hr (cubic meters/hour) which in actuality bears no relation to it's ability. Note the testing methods employed
here and
here. Even though the second testing method may seem a little primative, both are more representative of real-world usage.
Examples of "good" fan construction/design allied with quiet operation and longevity would be those from Scythe, Noctua, Noiseblocker as well as *some* Thermaltake, Sunbeamtech, CoolerMaster and Gelid
.
