System fans aren't the most exciting PC components, so we rarely cover them here at TR. However, there are some fairly substantial differences between the various options on the market. There's also a staggering number of different fans. Hardware.info has combined over a hundred 120-mm units in a massive round-up that compares cooling performance, noise levels, and efficiency.
The efficiency stats are perhaps the most intriguing. Hardware.info cranked each fan up to 30 decibels and then measured the resulting airflow. Spinners from Enermax, Noiseblocker, and Corsair fill out the front of the field according to that metric.
Cooling performance and noise levels were tested with the fans running at 7V and at 12V. Interestingly, the standings are quite different for those two voltages. The quietest and most powerful fans at 7V are not the same as the best ones at 12V.
Different fans are good at different things, so the comparison concludes with a series of recommendations based on whether you're shopping for a high-airflow, low-noise, or budget-oriented spinner. Even outside the budget category, some of the top units are surprisingly affordable. The whole round-up is recommended reading.