CPU fan purchase points

Fan size
The 80-inch fan has large blades and naturally large air volume, and can take away more heat per unit time. It is easier to achieve good heat dissipation effect with a large heat sink. However, for 80-inch fans, the contradiction between wind pressure and noise is more prominent. If a larger wind pressure (that is, a higher speed) is required, the noise problem will become very serious. However, if a silent fan is used, there will be a problem of insufficient wind pressure. If it is used on a heat sink with denser fins, the wind will not blow to the bottom of the heat sink. Therefore, most of the radiators we see that use 80-inch fans will be used with large radiators with sparser fins. Typical products are Coolermaster HV81, Tt Volcano 9, Tt Mars 3 and Kyushu Fengshen AE2388+.
The 60-inch fan has smaller blades and a smaller air volume. However, even if the 60-inch fan reaches a higher speed, it will not make too much noise, so the 60-inch fan is easier to generate a larger wind pressure. Choosing a well-made 60-type fan and matching it with a small radiator with denser fins can often achieve a very high level. Typical products include Kyushu Fengshen AE070+, AVC 112C86, and AVC112C83.
The characteristics of the 70-type fan are between the 60-type and the 80-type, which is relatively moderate. But precisely because of its unremarkable characteristics, not many manufacturers use it. Representative products include Coolermaster's 7H53F.
In summary, if you want your computer to ensure the cooling effect under the premise of silence, you should choose a 60-type fan and match it with a well-made heat sink. The most representative products are naturally AVC's 112C86 and other products. According to my practice, if Kyushu Fengshen AE070+ is replaced with a better quality 60-type fan, it can also achieve a very high quality.
Other factors
In terms of bearings, SUNON's magnetic bearings and AVC's hydraulic bearings are the most advanced technologies at present, but unfortunately, the price of magnetic bearings is too high, and almost no manufacturers use them (if you see such fans for sale one day, don't miss it); and AVC's products are only used in their latest products, and they are rare in China at present (AVC's channels are really not very good). Others are double-ball bearings, which are better, while ordinary sliding bearings (also called oil-containing bearings or oil-sealed bearings) are obsolete products. Some domestic manufacturers are still producing them, but there are many problems, so it is best not to buy them.
In terms of fan blade shape and number of blades, in order to achieve the purpose of silence, of course, sickle-shaped and as many blades as possible are preferred. But many famous brand manufacturers' products do not care much about these aspects, because these factors do not affect performance as much as bearings and speed.
In terms of air outlet, I am not optimistic about centrifugal fans. Under the premise of the same noise, its air volume and air pressure are not as good as axial flow fans. Only those who like to try new things will choose innovative products like Coolermaster's Tornado series, and according to the feedback from those users, the results are not ideal.