I love a lot of cars, to be honest, but I had a lot of fun in the RE Amemiya µ Boost 7 (the premium that isn't the GT 300), and last night I tried to have an online race in the 350Z Z-Tune, but got disconnected shortly after being forced off the track by someone in an NSX who rejoined the track without looking, so I never really got into it. Also everyone was using racing softs so it kind of made it boring.
But the car I enjoy most would be the RX-7. No, wait, it's the ARTA NSX.