My favs are:
Adeliade Street Circuit: i am a specialist on this circuit, ive done more laps here than anything else ever. I know this circuit back to front and love it totally and unconditionally
Spa: its just a classic track, everyone would agree with that
Valencia: i actually hate this track as it has no really good overtaking spots, but its one track that ive learnt back to front due to online racing, so i have developed affection for it
Laguna Seca: not sure why i like this one, if it had a longer straight in there somewhere it would be perfect
Gold coast indy Australia: something about this circuit attracts me, and its familiarity only increases its appeal.
Mugello italy: just a different track, has a good flow