Out of the Le Mans Prototypes, I think the best overall race car is the Mazda RX-7 LM. It handles incredibly well and has excellent acceleration, top speed, braking and cornering. Without doing any modification, I can outrun race cars like the McLaren F1 GTR on races set at difficulty 10 (175 A-spec pts and over).
By the way, it's the car I prefer to drive on any given track and in LAN racing.