"TrunkTrackerII" is one of the previous incarnations of the Uniden trunktrackers. I can't remember what the exact difference between 2 and 3 is, but the 4s are digitals (I believe). 3 is the 246T and some others. Whether a 2 works or not for you, depends on where you are, and what you want to listen to. Your trunking systems will determine what you need to buy.
The Radioshack Pro-96 is an excellent radio, but is expensive. If a scanner can listen to it, the -96 will almost certainly work. Many, many, many threads deal with the features of the individual scanners. To answer the second part of your question, the Pro-96 will be MUCH better than any of the Unidens which feature "TrunkTrackerII". BTW-That's just a way of naming the trunking ability, it's not the model name of the Unidens (which will be like BC785D, BC796D, BC780XLT, etc...).
*EDIT* After further review, it appears TrunkTracker 2s will do EDACS and MOT, 3s will do LTR, EDACS, and MOT. 4s will do 3s + digital.