My favorite track in the game, and in real life, is by far Laguna Seca. I think the sheer fact that even after racing it countless times, I still spin out occasionally on that Corkscrew, and I still overshoot the final turn.
Monaco is okay, but that track in my opinion is out of date. The F1 cars that race on it are extremely wide. There's no room for anyone to pass practically. I've watched that race in real life, and most of the time, one of the first two qualifiers ends up winning, in fact it's almost always the first qualifier. To me, the 8 feet wide F1 cars that race on it are just too wide to have any real competition. The 4 feet wide cars of yesteryear, now that was a race. Amazing competition, very technical track. But now, I personally think that track is just too tight. If you watch the race in real life, you'll notice that their gears are set so low it's almost rediculous. On that long straight after the 90 degree right turn, they literally change gears every 3/4 of a second, redline in 6th gear before they even get to the chicane, and then turn. Now there's nothing wrong with that of course, but I just think that a track like that needs to have wider lanes to make it really interesting. Anyone past 4th or 5th place may as well not be racing, I'm sorry to say, especially when there's 40 cars on the track at the beginning of the race.
But that's real life, I love Monaco in GT3
Oh, and Monaco as we call it is actually Cote d'Azur in the game. It's in Monaco in real life and that's what most people call it.