Maggiore GP is my favourite fictional track due to THAT BANKED HAIRPIN!!!
In all seriousness though, Maggiore is where I believe that any car can be strong there, unless we talk about Gr.1 that is, those poor Group C cars couldn't stand a chance at all! Basically it's a balanced track for both Gr.3 and Gr.4 cars with fast flowing corners and some long straights to stretch the legs of those straightline speed cars.
The Tokyo tracks were a bit of a double-edged sword in my favourites list, as I liked the tracks at night when it comes alive, plus the high-speed nature of the tracks (Central Loop tests your pure momentum, East Loop adds top speed alongside momentum, and then both South Loops are basically East Loop mixed in with that Central Loop feeling), but then it's a circuit situated within a highway, which meant the only runoff areas are some blocked off offramps and surface extensions, which meant that these tracks were pretty much SR traps for the most of the time.
DT Seaside is probably another optimal track for the Gr.3 BoP to shine with bright lights as it's a fast-flowing power track, but then the handling cars can have a capacity to tear through the Chicane of Death flatout.
Sainte-Croix is where I can simply drive the Huracán GT3 and R8 LMS with ease, though Tokyo South Outer Race B made me really good swinging the Huracán around the 90% walled circuit. It's also the track where, at least in the C layout, Group C cars can race in harmony, at least that's what I think on top of my head...
Kyoto Driving Park is basically a testing ground turned into an actual race track that is really good, especially with handling cars. You'll see 86s, Caymans, Megané Trophies, 4Cs in either racing form, RSRs, WRXs, Evos, Beetles, FT-1s, even the bloody GTI VGT can battle against each other in their respective classes!