The Pro/4A isn't very good at all. That's all I know.
The 4AA is better, but still not the best.
The 4AAA is the best of the three, and I actually have it. It has a natural, balanced, and detailed sound, with slightly rolled off treble. The soundstage is absolutely MASSIVE and the instrument placement and separation is really awesome. They have a performance-like quality to them. Definitely recommend them.
Be CAREFUL though: there are many different drivers. The Series 1 driver sounds the best, and is symbolized by a black AND white diaphragm. The Series 2 driver is the same shape, but all black. It's slightly darker and has worse treble and a slightly forward upper midrange. The Series 3 and 4 drivers are still in production and are for the new 4AA and the 4AAAT respectively, and they're by far the worst sounding. The Series 3 driver is also found in the 4AAA Plus model.
You can't tell between the series 1 and 2 drivers on an auction photo. It's too fine of a detail; you have to look very closely at the outer part of the driver in person. You can, however, tell if its a series 3/4 driver because the headphone will have a different looking baffle plate. This picture is of the driver to avoid:
Hope this helps.
EDIT: ****, I just realized this is 2 years old. Oh well.