Well, i´ve driven lot´s of cars over this years. I´ve some experience driving fast and i have gone to a few BMW training lessons.
All in all, LFS is the only simulator were i feel comfortable with the handling of the cars.
Haven´t tried iracing, but in LFS the response of the cars, the feeling on the steering wheel, the FFB, the weight changes, etc. feels pretty realistic to me and way better than any other sim.
The extreme set´s may be difficult to handle, but according to what i have learn from guys who has experience in racing, the car´s set for circuit behave in a similar way to the fast set´s in LFS.
Also i love the way LFS manages the behaviour of the car according to how you use your tyres and how you heat them.
The physics are not perfect... well, scawen is working on that and till now he has done a better job than most of the big software companies out there. BTW, i also own Rfactor and i got bored of trying to get the damm thing work properly. I only use it now to make some laps on the F1 circuits before the races and since i got F1 2010 i am not bothered with that either. (btw, F1 2010 is awful regarding car control)
My last try was NFS shift 2 because i wanted to try some of the circuit´s..... After and hour i quit full of frustration and it´s suppoused to have direct support for my G25