I believe the digital ones give you actual numbers to work off of, where as the analog ones only give you a light spectrum too show where you fall. I could be way off on this, but I believe the analog is a constant reading of rich or lean updated every time the computer makes and adjustment to the ratio; a digital gauge tells you numerically what your average ratio is at a given rpm and engine load, much like the A/F meters on a dyno. Analog gives you a much more user friendly idiot proof red light/green light way of knowing if you're running good, while with digital you have to know what your ideal ratio is and tune the car based on the hard numbers. This is much better for tuning a forced induction or N2O car, since usually you already have an ideal ratio number to shoot for based on your application. Don't quote me on any of this! but that's been my understanding of it.