Belt Vs. Shaft
Here is the most detailed diffrences that I can give you.
The advantages of a shaft driven car is that it is more closely to a direct drive then a belt. A shaft can't stretch our or skip. You can still use a center and front one way with both belt and shaft. The biggest disadvantage with the shaft is torque steer. You don't notice it that much in stock and spec 19T mod, but the few times I have ran a 10 single mod motor in my TC3 if I pulled to hard on the throttle during initial acceleration the car would wonder slightly between the torque steer and me trying to compensate for it.
As far as the belts go, the only advantage I have seen is that they tend to be a little more balanced, and this is from how the motor is installed in the car. With a belt set up, typicly the "Torque wieght" will lean between the front and rear of the car. With a drive the torque wieght will lean side to side, and that is what causes tourqe steer. As far as maintence is conserned, belts usually have more things that can go wrong. See, with a belt you have to make sure it is at the proper tension. Too lose the belt will skip and slip, and the action is like doing a burny.....the tires are moving so fast that your speedometer is reading at 40 mph but your doing maybe 3. so thearetically, the belt is spinning at 20 mph, but the pulleys at the axles arent moving. If you set the belt too tight, then it's causing too much drag and slowing your car down, plus making your eletcronics work harder then it needs to and causing them to get too hot. As with a shaft, they typicly "float" in thier out drives, much in the same manner as the CVD's on the inside part of your car where it meets the out drive.
The only 4wd cars I have are T-maxx, E-maxx, and a TC3. I prefure the drive shaft because of it's reliabilaty. Iv'e seen a few belts on X-rays and Losi's during a race, as well as belts being too lose or too tight and that's what turned me on to the shaft driven car. That's why you see all 1/8 scale buggies are shaft driven, the belt wouldn't handle all that power!!! I may try the XXX4 as soon I get some funds up, but if Associated comes out with thier 1/10 4wd buggy before then I'll get that instead since I'm sure it will be shaft driven. I hope I shown some light on your issues there.