yeah, right now i'd say LFS is the best simulator. nkpro is very buggy in its current state. I don't know when 1.03 is coming out... but look out for the netKar Pro 1.03 demo. The lfs demo is sp/mp and lets you try out 3 of the normal streetcars and 2 tracks; blackwood (forward and reverse) as well as the carpark, though you can't put down any objects or make autocross layouts in the demo.
If you are only gonna play offline, rfactor would be the best choice.
If you are a rallyfan, Richard Burns Rally is a mustbuy. I just uploaded a vid of me playing RBR.