It depends what ones expect from racing game/sim,
I had 2 Cayman GT4 CS race yesterday and other then being bit weird on wet ( not that I could compare to real life ) it feelt good, AI was competitive and enough of a challenge for me, and no WTF moments,
yes, on Zolder for what ever reason they were much slower ( on the same settings) then on earlier tracks, which is still a shame that SMS didn't managed to balance this out
but to be fair, with this many cars on this many tracks, it takes lot of time to get it polished, when compared to few cars on few tracks
after that I played Forza and I turned it off with disappointment after 5 minutes, cars in there are just sliding all over the plate, no real sense of grip/lose of grip.
for me personally PC2 is close to being the best racing game out there, becasue it has lot of great stuff in it, that's still missing in some other titles
RF2 is certailly nowhere near as good, becasue it feels alpha stage with absolutely un-balanced visuals ( new stuff looks great, but oh boy some of the old stuff looks really bad)
AC feels good overall, but doesn't really have deeper career more, and yes I will say it again, weather progression and night
AMS is great for what it is, taking advantage of good GMOTOR engine, and many many years of polishing of that engine, but it's old looking and while the content is unique - which can be positive to many people - it can also be negative because simply you are missing lot of your favorite cars & tracks
so if you wanna ask, what would be my top sim/racing game,...
well, I think it's probably
Gran Turismo Sport! physics is certaily realisic! visuals are second to none, proper racing series rules and all that, tracks that feel alive, and it's all so nicely polished ! also really good livery editor , something that was missing in a long long time
only downside to it is lack of content and as well as AC, nothing is dynamic
my dream racing game would be combination of
Gran Turismo Sport, PCARS2 and Assetto Corsa
GTS&PCARS for the visuals, overall presentation, car & track lists, weather, etc.
and AC for how smooth if feels - especially on gamepad - and the "ease and power" of modding ( when compared to other moddable titles)