I'm gonna give some recommendations on cars to use for the tournament.
Mercedes SLS AMG
Car accelerates fantastically. Grip is amazing, top speed is fantastic. Very forgiving car, it'll only slide if you want it to. I've never spun out. Best all-around sports car in my opinion.
Nissan GT-R SpecV
Specifically the SpecV model, this car can turn so well to the point of where your eyeballs might not stay in. You know those fancy headlights that turn in the direction the car is steering? Nissan was gonna put them in the GT-R but it turns too fast for them. It's a very quick car, accelerates great, top speed is great, but don't trust it too much when sliding, it might bite your ass.
Lamborghini Gallardo LP560-4
When fully tuned, the baby lambo is probably the most slidable car in the game. It's an absolute blast because it's addicted to sliding around every corner in a perfect manner. Sometimes it can spin too much, but it's rare, and if you're handling it right it's a total blast. Top speed is good but acceleration could be better. Braking is a bit slow. If you're looking for total grip though, I'd look elsewhere, this car is slippery in a good way.
Ferrari 458 Italia
Decent all-around GT racer. Acceleration and top speed are great. I suggest not trying to slide it; it's more difficult than you think. Grip is a bit mediocre. Other than that, turnability is a bit of a pain, a bit too much understeer. Looks great and is fast and quick though.
Ford GT
Fast. Faaaast fast fast. In fact, 815 HP when fully tuned, to be exact. The car is somewhat quick but top speed is great, but because it's a midrear car AND because it's a big fat heavy american muscle car, it has loads of understeer stock, but with some racing slicks and a few suspention modifications it's a whole world better. Still not as good as others, though. This car also sounds like it's going to eat goats for breakfast.
Chevrolet Corvette ZR1 (C6)
When fully tuned, it has slight understeer but slides well to make up for it. It's a quick car, and it's top speed is mindblowing for it's type. But it's still an american muscle car so the acceleration isn't AMAZING, and the understeer can be a big pain sometimes. The racing modified version is fantastic but RMs are prohibited in the tournament.
There you go.