You will often find used T4 & B4's readily available but I believe it has more to do with the fact that they sell more T4 & B4's then similiar Losi products. I am not saying AE is better than Losi but I believe they hold the majority marketshare.
Personally, I always base decisions like these on race results and if you flip through this months RC Car Action you will find the results from the Hot Rod Hobbies ShootOut which I posted below:
Factory Mod Buggy
1. B4
2. B4
3. BK2
4. BK2
5. BK2
Factory Mod Truck
1. T4
2. T4
3. T4
4. T4
5. MF2