The tracks I want back the most are SSR11 and Rome.
I was playing GT3 recently with an F090/S on SSR11 and it was just beautiful... It flows extremely well and it is such a fun circuit to play. SSR5 is okay but 11 is much better. Later on while playing Formula GT I played Rome with an F094/S and that was brilliant as well. I really miss that track.
Grindelwald never really stuck out for me in GT2, but probably because I didn't play it that much. Red Rock Valley was pretty cool though. I'd like to see both these tracks return as well.