Having a Pro4 and nothing else as high-tech, you probably can't use my biased opinion, but here it goes. The Pro4 is a great, high quality car that can take abuse. The main difference between belt and shaft, is that shaft has amazing acceleration, while the belt's changing tension makes acceleration much smoother, and less harsh. When it comes down to shaft vs. belt, it's just personal preference. I do have a HPI Pro2, which is a belt car, and I can definately tell the difference in acceleration. It's much more direct with shaft drive. As for what cars you should be looking at- I know this really doesn't help your decision, but look at all of them. Any of the commonly named cars on this forum are all more than capable, the newest design being the Hot Bodies Cyclone. All the cars have their own forums on here, so you can read up about each. But a big point that is always said with questions like this is parts support! Make sure your hobby shop has parts. Lucky for me, my LHS has nothing for touring cars, only monster trucks, so I could pick whatever I wanted. I picked up a used Pro4 on here, and couldn't be more happy. The car is very nimble, but planted. If you look at other cars and still decide you like the Pro4, check out this car:
It includes race quality things are an AMAZING price. I am not the seller, so I don't know anything about it other than what's in the listing. But I suggest you take a GOOD, HARD look at that deal. I bought my car as a roller for 225. But who knows, you may find a design you like better from some other company. And ask around at your track to see if you can turn a few laps with someones car. It doesn't hurt to drive it before you buy it...
But good luck with whatever you pick!