So I threw myself into pCARS quite early (feb 2012) and found it exiting at first. A lot of "good" talk of plans and ambitions in the forums. On the road, the first cars didn't do too bad, actually. It showed some real potential with both the car physics and dev attitude/ambition.
At some point it took a turn in the physics where I suddenly couldn't continue to like it. I went through the setups over and over again to find the sweet spot but the whole experience just felt inverted and awkward.
Then came AC. I felt at home. Just like LFS, but with a little more magic in some areas. pCARS started to collected dust, but I followed the forums.
Now, pCARS is considerably better again, and I enjoy a race every now and then, but I'd say I do 1 pCARS race for every 10 in AC. Mostly, just to check and compare if there's been any changes for the better. And now with some activity in LFS I enjoy being back on Westhill (and the other tracks). pCARS serves a lot of bling and a more complete "racing event/career experience", but for me, it's the time on the tarmac that counts and in that area both LFS and AC shines brighter. On my rig, in my brain, I should add.