I think TRD3 covers almost everything TRD2 had (a few cars missing) but since TRD3 is bigger, I would go with this one.
Great memories. Above all else, my personal discovery of online play, with features still missing from every PS3 racing game I know.
Beware, however, the physics, even in PRO SIM, aren't really up to sim standards. But the variety of cars and the impressive track list make up for it.