iRacing is the best as far as sims go, but as mentioned the price.
netKar Pro is ok, feel/handling is great but the rest of the game seems a bit sketchy
LFS is ok, bit old now
rFactor can be very good if you spend eleventy-billion hours downloading mods/plugins etc, as stock it's shockingly bad.
C.A.R.S is very much alpha, and doesn't seem to be progressing particularly well into a decent sim, I wouldn't bother paying anything for it just yet
rFactor 2, not out yet, I think the beta entry is 'simply' buying the full game, gonna be interesting to see what it's like as stock.