TambokGT:
In regards to trucks, I own 3 rc10gt A-mains, 1 RC10GT and 1 XXXNT. Heres my take:
Since you stated "racing", your choices are narrowed down to companies AE and Losi. I operate a track here, and of the many trucks that come through I haven't even seen the mugen in person yet. Not only that but local hobby shops nearest to me
(3 in a 2 mile radius) doesn't sell parts for the mugen.
For durablity, and ease of maintanance nothing is wrong with the associated. I really like this truck. Go for the Factory Team kit RC10GT non-pullstart model. and then add your own .12 powerplant, servos, Fm or PCM radio. The Associated truck is extremely reliable and an makes an excellent choice to get started on offroad track with. Jared Tebo won a National Race with RC10gt, so I know they can hang. I do not recommend buying the RTR kit because you will have to upgrade bushings to bearings, the motor, the servos, the radio.
For better performance and excellent handing go for the Losi XXXNT or XXXNT AD edition. Both are what I consider the best truck currently made today. One setback to the XXXNT is that it is labor intensive if you have to rebuild tranmission.You have to literally take apart the entire rear end to get at it. After doing this about 20 times its enough to make a grown man cry!
So if you buy this one before you leave the hobby store buy the RRP hardened aluminum diff gear and install it when you build the truck. Also the battery box is a weak link. In the machine shop on my campus my son made a brace that strenghthens the battery box . Other than that it is an excellent truck. Do not buy the XXXNT sport RTR because you will still have to upgrade it. Buy the model and build it up right!
My son liked mine so much he bought a Drake.
The A-Main Chassis was an older Aluminum racing chassis designed by A-Main Racing products back in the day. similar to the XXXnt style lower chassis plate and upper deck structure. The company is no longer in business.
All of mine have AE components A-arms, Tranmission, ect on it. and for ultimate durability This is the way to go. Imagine an RC10GT with a Losi Like Chassis structure. I have NEVER broke a part on one of three of these models. All three of mine are in-destructable. Since the company no longer exists I have considered milling a few chassis to keep as spare should I ever need a chassis part. but otherwise I can go to any hobby store and buy AE part to go on mine. I have only seen 1 amain that had losi components on it and I am waiting on my friend to offer to sell it to me.
Now to address the others: Traxxas, Duratrax Carlson(german) all make rtrs (yes they are fun), but you will have to spend some coin to seriously upgrade them to "race ready"
Hopefully whatever you get Just have fun!
chris