If you get the Losi, make sure you get the graphite series since that one has the revised belt. The Losi is a very worthy car. Takes a beating well and also has a stiffer chassis.
With the TC3, there is torque steer that people compalin about, because of the drive shaft. I really don't know about that first hand. Another complaint is the fron dynamics of the car.
As you may already know, the settings on an on-road (caster, toe, camber) are very important to the way a car will perform. When the front of the car is in a collision or hits the boards, the settings WILL change before the Losi will. What some people do is adapt the front of a TC3 to a Losi. Chassis wise, the TC3 chassis has more flex in it. What others do is upgrade to the BMI chassis to get it more rigid. The TC4 is just an upgraded rear suspension when compared to the old one, plus a few mroe bells and whistles.
If i were you, go to your track and observe what cars they use and ask them for their opinions on the cars. IF possible, try them out but remember, driving someone's car is like letting someone kiss your wife or gf and I'm not talking about a peck on the cheek. Don't be so eager to ask if you can try the car.