The Tekin will be the best for racing, with the Xerun second and the Castle Mamba system being flat bad. The castle is probably the best system for pure bashing.

In short: Castle is sensorless and generally overpowered for racing. You'll probably need to add a BEC if you run the Castle. The Xerun is a good system, but the motor runs a little hot and the ESC is an extremely tight fit in Tekno vehicles (go look for pictures of the modifications on this and the EB48 thread before deciding to buy it, so you know what you're getting into). The Tekin stuff fits perfect and is probably the most popular race package, and still has gobs of power.

At those prices, I would put the Tekin as my first purchase, since it would do both things well, and probably the Xerun as my second option since it will do both decently as well and is cheap.