...Or you could use one of the pulse switches that GrizzlyT mentioned above, and it would take 2 poles. But it would take some crazy custom programming with AutoHotKey, and would only tell you if you were turning it up or down. (is that right Grizz?)...
Well, I'm not sure it would take any crazy programming. (Not any more than any other switch.)
It's basically just 2 momentary switches. It has very light detents that, as you rotate it, triggers the momentary switches. I think there is aprox 12-15 detents per revolution. So, if you rotate the knob CW, then one switch will "pulse" out momentary switch closures for every detent and the other switch will do nothing. Rotate it CCW and it's reversed, with the second switch sending out "pulses" and the other one does nothing.
The three type of rotaries you have mentioned have different applications and limitations. You need to ask yourself what it will be controlling?
A. A
potentiometer (pot) can be wired up to the A-Pac and other controllers. However, doing so usually assigns it to an axis (X,Y,Z,Xrot, etc.) If you want your rotary to control an axis, for example to control a rudder, then a pot would be what you want. It also depends on your software. Because some apps (like TM Cougar software) allow you to re-map the axis to keypresses. So, in a round about way, a pot
can control keypresses....just not natively.
B. A
rotary switch (Multi-position) is best used when each detent position has a different function, or uses a different keypress. (For example, a radar mode switch. Position 1 is ground radar, position 2 is air radar, position 3 is FLIR, etc.) Each position is a fairly stiff detent and it's own seperate switch, so depending on how many positions it has, that's how many switches you will need to assign/wire-up.
C. A
pulse switch is best for natively controlling keypresses, or when your software doesn't allow for an axis pot to be re-mapped. A regular rotary switch (Even a dual-pole one) will send out switch closures for each pole, regardless of the direction of rotation and they will all be toggle switch closures. Whereas, a pulse switch sends out momentary closures and only triggers one switch (pole) at a time, depending on the rotation. It would be for something like a range knob. Let's say the sim uses R for radar range increase and Shift+R for decrease. You map the CW switch to the R key and the CCW switch, to the Shift+R key.
Then, there is the limitations of your hardware and it's software. An A-Pac allows pots to be assigned axes and allow toggles....A Cougar allows pots to control axes and to be re-mapped to keypresses.....a USBKeys does not allow either pots or toggle switches.
So as you can see, it does really depends on the limitations of your controller and what you are trying to control.