I have been building and modding rc for a long time now and can say this that any company that is looking to build winning car or truck should look at the drive train and how to use it as clean and as simple as possible. That being said.
If you have drive lines that use one for the front and one for the rear and then use a gear on both to make it turn that is about as simple as it gets. Now the lay out to get balance with this simple drivetrain is going to change how the rc handles the weight that is being used. Center of gravity and then shock and suspension geometry come into play. keeping this simple and strong will have you a winner on the track and with customers. As 4wd go I have two that I have bought and one that I designed and built, that are 1/5 scale and I can tell you that there are things I look for first, then I go about upgrading the short comings the rc has. Everyone has there favorites as to what that they like to work with in doing this Mine is 7075rc as for the two 1/5 scale that I enjoy they are the Redcat XB-E and the Losi 5ive. There simple in design and they hold up with some mods that I added as I used them. The XBE took the most mods right off as it need the bearing carriers(hubs) servo almost before the first lipos ran out of charge. I knew that before buying it for the most part and that I how I found 7075rc. The only thing That I want to try on it know is the losi 5ive shocks on it. As for the 5ive, the steering servo went to the breaking and a stronger servo went to the steering the pipe was bought with the truck (new), and so power was always pretty good. I know run the Gizmo full mod with the matching pipe that can come with the package deal. I like the torque that it offers over the OBR full mod that is the same size. I enjoy both buggies and it's hard to pick witch I like better as they are very different from each other. The XB-E is pure speed! And the losi is a great handling and very scale truck.