Agree with Mark. If this is your first GT12 then the Schumacher GT S1 version is the one to go for. Everything you need to get a competitive car is in the kit; it builds easily and first time; the instructions are excellent including set-up tips; it will take all the knocks you could reasonably give it; it takes the class-standard wheels, tyres and bodies.
The S1 chassis on the old car was plenty stiff enough and tough. Having the right springs and a diff will make it easy to get driving, things you don't get for that price from any of the others.
Be aware that the servo mount positions will not accept any of the Futaba-style mini servos (a mistake in my view) so you will need to confirm that any servo you already have will fit. If you don't have a mini servo, the Core RC one is good value.
If you already have a GT12 and are looking for something to upgrade, then any of them will give you a good drive. If Santa doesn't have to bring you a new kit in a box, think about a used Schumacher SupaStox. HTH
