Chaparral 2J and Sauber Mercedes C9 are still my favorites. Pump up the 2J and it flies. The C9 is a road dominator.
The Plymouth XNR Ghia Roadster '60 with it's Mondo Beyondo styling, once you harden up the suspension a little and fully mod it to 504 pp, I think, gets around the track pretty good. I haven't raced it online so I'm not sure, but it easily waxes 650 pp computer cars. I wish PD would give us the Speed Test back. At least that way we could tell how fast cars were in a straight line for comparison.
And paint the XNR silver, the stock colors kill it.