Live for Speed looks pretty good. Is there multiplayer on it? (I suspect yes?), and can you customize your own car?
Multiplayer is what LFS is about. You can't customize cars like NFS, it's a sim. Sim and multiplayer gameplay first, everything else second. There's a custom car editor available, but it's kinda buggy (no support from the devs, same as AH) and the next one that's supposed to be well polished is due out but with no due date.. Probably sometime after the next coming patch is out. There is a NASCAR mod that is worth checking out though.
I suggest you sign up for a few leagues.. I haven't been in one or even played LFS for a long time now, so I can't recommend which ones. But they're great fun. Guaranteed fun when you find the right ones.
And gameplay on demo servers isn't representative of licensed ones.
Mazz - You mean GTR? LFS is way ahead of F1 nowadays. iRacing and it are the best. Only LFS is cheap and easy to play, whereas iRacing is expensive and pretty anal. The small edge that iRacing has over LFS in physics may be negligible after the upcoming patch is out.