been there twice for F1 Grand Prixs, and many more times for other events like 24Hr, Porsche and Ferrari Days, even been lucky enough to get a ride around the track in an F40.
On the 2 times went for Grand Prixs, first was stood on the hill at Stavelot, and the second time in the trees at the Bus Stop, but walked round for a track invasion infront of the podium. I'd personally say to go for Eau Rouge, its a monster in real life, every time i went still was :O at the sheer size of the thing, plus you're in a good place to then invade the track (if still can) after the race.