I cant really decide whats "the best" as every car is good in its designed environment, so here's my top 5;
Number one, all time fav; 997 GT3; Quick all the time, perfect throttle response, awesome suspension, so settled regardless of speed. I adore this car and am honestly a little bit sad every time i get out of it. The sound of it on cold start really says "yeah im a porka, but im not here to fu(k around" with nice lumpy cams that resemble a worked GTR rather than a refined german supercar
Number two, Lambo Gallardo spyder; It doesnt feel as fast as you'd think after owning a GTR, but its loud, quirky and the top down makes it a pleasure to drive even with the cumbersome gear shift surround
Number three, Mercedes Benz CLKAMG Black Edition; The factory issue buyers with a letter saying its a handful and to be careful so you know its good, great gearing, awesome seats, the noise is to die for, not for the feint hearted. This was more of a thrill than a pleasure. Its true, you need to be super careful of the loud pedal
Number four, Masarati GranTurismo; A real GT car thats a 2+2 seater, you could sit in this for 1000k's and get out feeling as fresh as when you got in. Nice subtle exhaust note, doesnt stand out like a Ferrari but just as nice on the inside. If you're a millionaire and need a daily, this is it.
Number five, Lotus Exige S (supercharged); A mission to get in and out but the pain (literally, your sides hurt) is so worth it. Very responsive, awesome noise, very trackday spec inside yet still has aircon and power windows. If you're looking for corner speed, you found it
Other notables include the new R35 GTR, Rolls Royce Phantom etc but as biased as this would sound, nothing has felt as fast/scary/fun as my own R32 even though its a beyotch in traffic with the clutch, very noisy all the time, rock hard suspension, no aircon etc Id love to have a go of a late model GT2 on slicks one day, that would probably be the ultimate/best thing as far as niceness on the inside but with insane corner exit speeds and overall respect for the throttle