I have 3 and 4. 3 is my favorite, I've played it the most, the driving mechanics of 4 is a bit different, not necessarily better or worse, just different.. There's better mechanics of body roll and traction on 4. You can really feel your differential slipping and all of that.
4 is cool because I've raced a few hours today and leveled up with Nissan to give me all free upgraded parts. So no more 100 races on the same track so I can afford race upgrades!
I like 4 I'll be playing it more for sure.