Top speed-wise it's the Ferrari 599XX Evo, acceleration-wise it's the Shelby Monaco King Cobra. If you're just starting out however and you don't have the Car Pass, the Ultima 1020 Evo should serve you well.
IDK the fastest but using drag tires improves the acceleration and launch a lot and that also high braking and grip is also important since fast cars might need to drift at fast turns.
@Ex-Driver 2887 I got the barrett-jackson car pack specially for that car, and u weren't lying, that babe drives like a dream, one tunnig later, omg the fastest car in my collection, thank you.