I absolutely adore ACC and have been racing exlusively in this sim for several months now. That being said though, I've been racing online only and on PC.
I have heard several times from different sources that ACC has its problems on consoles, being it crashes, weird updates etc.. The AI and the career mode is okay-ish I guess, but the real value is in its multiplayer, if you ask me.
AC on the other hand is an offline content fest (again: only speaking for PC). I have only ever played it fully modded though. The unmodded graphics speak for themselves? :)
If you only want to drive offline, having a nice career mode, challenges, etc., I would wait for AC Evo.