In terms of on-track performance the Analog and Digital controllers would be hard to distinguish. Both provide a high resolution, stable (jitter-free) signal to your sim, which means very accurate precise detection of your wheel and pedal input. The analog controllers use potentiometers for position sensing, they work by reading the resistance change when you turn a shaft. A metal wiper with either a carbon or conductive plastic conductor is actually rubbing against a disk inside the potentiometer. With this kind of friction, over time a potentiometer will degrade and go bad, which you will see in your game as erratic behavior in calibration or in your control input. To combat this, we offer replacement potentiometers, and make changing them out very easy (instructions are provided in the user's guide). We offer two different grades of potentiometer, the DK pot is a carbon element pot with an approximate life span of 6 months to 1 year, the ETI pot uses a conductive plastic element, and it has a life expectancy of 1 to 3 years.
By contrast, the digital controllers use an entirely different method for position sensing, called an optical encoder. These devices look similar to a potentiometer, but they detect movement in a different manner. Essentially a wheel with tiny pinholes in it is being turned when you move your wheel or pedal, a light beam inside the encoder passes through those pinholes and the encoder reads how often the beam gets broken. Because of this, there is no friction, and thus no wear potential. An optical encoder should last you for as long as you own your controller. Also, being a digital device, there is no analog to digital conversion needing to be done to translate the rotation to the computer. With the analog controller, we need to use an antialiasing algorithm to clean up the signal of the potentiometers which would otherwise show up in your game as jittery behavior.
Lastly, though it's not a huge factor, the digital controller does provide a higher degree of accuracy vs. the analog controller. In the steering, the analog controller provides approximately 800 to 1000 steps of movement from lock to lock, while the digital controller provides approximately 1500 steps.