Road America. One of my favorites. At the moment, my favorites(in order) are:
Road America
Rio Coast Loop
Bugatti Day and Night
Lime Rock
Nurb Full Circuit Day/Night/Rain
Silverstone all versions
The Glen all versions
COTA GP circuit
Nurb GP Day/Night/Rain
Sebring Full Night and Rain
I want to like Sonoma but, even in my CSL, the track doesn't come alive. In my opinion.
Yas is an awesome track but those really tight left hand turns in its design, screw up the flow.
Spa. I didn't rank it because it is an awesome track on its own. Each transition is otherworldly. Night racing is hairy and too real. The sense of speed is for real. Rain is just fantastic. The Sun just poking through and the mist... just great. It has everything I want to keep me tuned in lap after lap. I even feel it may just have the best positioned replay cameras in the game(Road America and Yas are awesome as well). This is just my opinion on how I'm loving this game.
Bathurst. After having visited a few weeks ago, driven around the road and walking on it and looking from the top of the mountain, no game will ever do it justice. That's just me. Now, if they made a Rain version....
The other real and fantasy tracks are just not doing it for me. Not to say they are bad. I'm glad there are those tracks for other users that like them. They aren't pressing my buttons.