Well of course the three fastest (non-Formula 1) and favorite are the Toyota GT-One Race Car, Nissan R390 LM (Calsonic), Mazda 787B LeMans winner. They're all so much fun.
Next would be the odd cars like the Mustang, Skyline R34, Audi TT, Calsonic Skyline, various LM 'Dream Cars', and the faster of the rally cars.
Least favorites are always easier ... `Scudo, Zonda C12, Miatas ...
*shrug* My opinion changes from day to day.
~LoudMusic