I like CTDP for F1 but I find you can wack a wall fairly hard and take no damage, so I tend to use FSONE 2006. But the AI seems worse on the latter, and the physics is @#$%&. I would say the handling is better on CTDP but that doesn't make it the easiest to drive.
Oh, and if you're using a keyboard, buy a wheel. In all seriousness.