Hi David, there are actually quite a few Amidol formulas out there to play around with. If you check out the unblinking-eye, ed has posted many formulas.
The differece between the formulas is like trying to describe the difference between various brands of chocolate. Sometimes the difference is as plain as the nose on your face, and other times, there are fine underlying nuances that you might need sometime to discover and come to appreciate. Some of the major differences will be the speed with which the developer works. The Smith formula, with a large amount of amidol, is very powerful and fast working, whereas a formula like that of Peckhams (which has less amidol, but uses catechtol as a second developing agent) is slower working, meanin the development times will be somewhat longer (for my exposure and development technics.).
The "color" of the final print and the depth of the shadows are two more areas in which difference can be quickly seen. Some of the more subtle things to look for would be the seperation in the mid-tones.
Selecting an Amidol formula is like selection a paper, a film developer , a film , a lens, etc...
There is going to be some experimenting involved. And after you get a feel for the individual components of a formula, don't be afraid to "tweak" the basic formula to make it more suitable to your individual needs.