So many choices, such little knowledge... (Case Fans)

The PWM thing has NO relationship to Static Pressure versus Air Flow.

There are two major types of fans on the market now. The older design, 3-pin fans, can have their speed controlled ONLY by varying the voltage supplied to them via Pin #2 of the fan header. The newer design, 4-pin fans, use a different method of speed control. In that design, the voltage supplied to the fan on Pin #2 is always the full +12 VDC. But the fan also has a new component inside, a little chip that uses the PWM control signal supplied on the new Pin #4, to modify the flow of current from that source through the motor windings, thus controlling its speed.

The designs are built to have SOME compatibility. The mechanical and electrical connections are very similar so you CAN connect any 3-pin OR 4-pin fan to any 3-pin OR 4-pin header, and it will work - sort of. For the mis-matches, there are two cases. If you plug a 3-pin fan into a header that actually is using the PWM Mode for control, it will always run full speed - it gives you good cooling, just no control over it. For a 4-pin fan plugged into a 3-pin header (or even a 4-pin header using the older Voltage Control Mode), the fan WILL run under speed control. It's just that Voltage Control Mode is not quite as good a PWM Mode for control of a 4-pin fan, from a technical perspective.

Completely separate from all that is the question of balancing pressure and airflow, and these considerations are determined by details of fan blade design and related matters. However these items are done, it can be done for EITHER of the 3-pin or 4-pin motor types. Any fan will have a performance curve of what airflow it delivers against what back-pressure that resists air flow. Often the "curve" is a roughly straight line (not perfectly straight) going from high airflow at no backpressure down to zero airflow at some higher backpressure. The specs of most fans will tell you those two end points of the graph - the maximum airflow at no backpressure, and the backpressure at which the fan simply can't move any significant flow of air. You never get BOTH max's at the same conditions.

"High Static Pressure" fans are designed to move lots of air against a modest backpressure, and are ideal for fans on radiators and heatsinks that have narrow air flow passages. "High Air Flow" fans are designed to produce substantial air flow against very small backpressure and are well suited to case ventilation. Intake fans always should have dust filters in front of them, but those filters offer only small backpressure restrictions as long as you keep them clean.

Noctua fans as a whole family have the reputation of delivering higher air flows at lower noise levels than many other makes, and carry a longer warranty period than most. They also are a bit more expensive. Their Industrial (iPPC) lines have their highest air flows, but you may not need that much if you are not building a high-power machine with lots of heat generated.

I recommend you ensure that the fans you choose match the capabilities of the fan headers on your mobo- that is, 3-pin vs. 4-pin design. But that capability on mobo headers can be tricky to discern. If you need help there, tell us what mobo - maker and exact model number - you have and we can help on this point.