A GT4 Photo Mode picture of the old 2002 Audi R8 race car flying down the Mulsanne straight. The title comes from the fact that, since it's inception in 1999/2000, it absolutely wiped the floor in sportscar racing, winning the 12hrs of Sebring every year it entered (2000-2005) and dominating the Le Mans 24hrs even when restrictors were put on it in 2005, and it now stands up with the Porsche 956/962s as one of the most successful sports racing cars in history

Here's my other favorites-
Nissan R92CP Race Car
Mercedes Benz Sauber Mercedes C9 Race Car
Those two are awesome cars as well, the C9 dominated sportscar racing in real life when it was around, and the R92CP is just a speed demon!