I asked my good friend last night how he liked Dirt Rally since he has both games and he said "It's fucking amazing!" Best Rally Sim he's played, only issue hes encountered is force feedback with his wheel. IMO Dirt games aren't made for wheels. Using a wheel for Dirt would fatigue someone in top physical condition it's so much work.
Also he was having a terrible time with Project CARS, said frame rates were allover and it ran like crap even when at 720p with low settings, total opposite of my experience at 1080p high settings, so he rolled back his video card driver and now it works perfectly. Something to keep in mind if you're considering it. Personally as of today I would not buy Project CARS if you expect to hit the ground racing. I've spent more time tweaking my wheel settings to make it feel somewhat like it should than racing.
Again game runs and looks amazing but the controls are absolute shit with a wheel. Most especially under breaking. I have noticed some cars handle better than others so I'm hoping its a bug issue that an update will resolve in the future but I go from Karts which breaking is terribly harsh, like 0-100% with a tap, to Formula A where breaks are like a sponge. It needs sorting out.