best 21st century DTM car would be the CLK. outplays my TT-R & A4 which have better torque at Nurburgring GP. i do have another one in the same year, Vauxhall Super Astra. its got some power upgrades, which i really regret to have done so --- it did result in worse handling than the stock CLK. M3 GTR...didnt bother testing it, as it just weighs too much. yet it had lots of trophies in her year -- and GT5 does weigh that factor to some extent, e.g. V12 LMR over GT-One, 908 over R10, all the Supras/Zs over GTR/NSX in JGTC, and the opposite in Super GT(do correct me on that if i were wrong).
those 4WD 90s DTM cars --- i love the sound, but hate the price. the 155 touring car was one of my favourite in GT2. and do try acquiring the 190E evo when u r piling up cash.
mind u, the CLK touring car just has a horrifically bad graphic depiction. just look at the headlights --- disgusting. compared to that, the Audis & BMWs were done with much more care. i dont watch replays, so i t doesnt really bothered me...but it still shocked me.