I went thru the same thing so i am talking from experience... my choices was a 2009 gtr, 2005/2006 carrera 2, 2009 s5 and the m3. After test driving all it was down to the audi or bmw, both were v8's. The Audi had more grunt but was more relaxed than the bmw and the interior and bulid quality of the audi was better. Porsche was a basic bottom line base model so ya...no way. The GTR??? hmmm fun but after a while i was embarrassed to be driving the car, it was the biggest car but it was the fastest by far. I chose the m3 cause i am a bmw fanboy and couldn't make myself buy an audi and somemore i would be buying the best by driving the M the audi was only an S not an RS.
Another choice was the R8, that is a nice car but it was going for more than RM450k not very practical car though. Met an r8 and Gtr on the road that day and played around a bit could keep up with the r8, guess it was a v8. The GTR "tapau" both our cars like we were stuck in first gear.