-What is the best PP-wise car?
Well, the Xanavi Nismo Z must be it b/c it starts off with the highest available HP of them all. However, I discount this one kinda for that reason. It has too much of a starting advantage, so the rest of my comments exclude it from consideration...
-Best-looking car?
Really hard for me to answer this one. I like 3 of them. In order, I'd probably say the Xanavi Nismo GT-R, the Petronas Tom's SC430, and then the Raybrig NSX.
-Best car to drive without driving aids?
For me, the Xanavi GT-R is the most stable by far. It handles like a dream and is sneaky fast, especially after the engine breaks in, after tuning the LSD, suspension, etc. of course. After tuning the Raybrig NSX, that thing handles like a force and accelerates like a beast. Without a good tune on it though, you'll be swapping ends real easy out of the turns.
-Best tuned up car?
No idea. I drive mine stock, but with oil change and racing soft tires, but my guess would be the Xanavi GT-R. I tune my Super GTs with the available tunes in some of the tuning garages here. Motor City Tunes has some really great tunes on these cars. His tune for the Xanavi GT-R is dynamite. He'll be posting a Raybrig NSX tune soon (in the middle of the tuning competition now) that I'm sure will be the bomb!