It's quite hard for me to pick favourites without listing almost every single racetrack I have come across. I'm the sort of person that prefers a game with 1 car and many tracks rather than vice versa. That being said, I have my 25 GB rFactor library open and my notebook of every racing game I ever played, so let's start *cracks knuckles*:
Favourite Real:
Albert Park
A1 Ring (now Red Bull Ring)
Austin (in reverse, thanks Codemasters)
Anderstorp
Adelaide
Ascari
Algarve/Portimao
AVUS (not a great track by any means, but I just love the oddness of it

)
Bathurst (loved it since TOCA on PS1)
Birmingham Superprix
Enna Pergusa (better with chicanes oddly)
Hermanos Rodriguez (with full Peraltada)
Imola (chicane or no chicane ok)
Macau Guia
Monte Carlo (probably favourite of all time)
Mont Tremblant
Monza (old combination track with oval)
Mondello Park (the only good thing about NFS Shift)
Nordschleife (duh!)
Old La Sarthe (without chicanes)
Old Fuji (before chicanes and Tilke butchering)
Old Hockenheim
Pau
Sebring
Solitude
Varano (from V8 Superstars)
Vancouver Indy (also from TOCA on PS1)
Virginia (especially North layout)
Watkins Glen
Yas Marina (in F1 cars only)
Zolder
Favourite Semi Fictional (real roads not used to race IRL):
Akina/Haruna
Hakone Turnpike
Irohazaka
Transfagarasan
Favourite Fictional:
Gran Turismo - SSR11 (GT1 version), Grindelwald, Seattle, Complex String, Citta di Aria, Costa di Amalfi, El Capitan, Trial Mountain, Rome Night, Eiger Short, Smokey Mt North, Tahiti Maze
Codemasters GRID series - Barcelona, Chicago, San Francisco, Dubai, Autosport Raceway, all touges (California, Hong Kong, Cote de Azur, Okutama)
Codemasters DIRT series - Croatia (DIRT 2), Monte Carlo (DIRT 3)
NFS - Proving Grounds (NFS II), Atlantica (NFS III), Olympic City (NFS UG)
Test Drive - London (TD6), Yucatan, Canadian Rockies, Mt Fuji, Vermont, New York (TDOR3)
Ridge Racer - Extreme Oval (Rage Racer), Wonderhill, Brightest Nite, Shooting Hoops (R4)
NASCAR Rumble - Night Flight, Circus Minimus
Destruction Derby RAW - Avalanche, Four, Karsutra, Leap of Faith
I could go on, but those are the ones that stood out most to me. You might notice some perennial favourites such as Spa and Suzuka are missing. Personally, except for 1 or 2 corners I found these tracks quite average. If you take away the history they don't really stand out to me.
As for fictional tracks, I find it a shame that a lot of modern arcade racers are now open world. It's fun from an exploratory point of view, but track design suffers and ends up being unmemorable/repetitive. From a sim racer point of view, PD seems to have lost their touch in making fictional tracks. Codemasters remains the only dev that still makes great fictional tracks.
Worst Real:
Any modern Tilkedrome (except those listed above, obviously)
Any city circuits that is constant 90 degree turns and chicanes (Singapore, Valencia and almost all Formula E tracks for example)
Any oval that isn't Indy, Daytona, Talladega, Pocono, Bristol (sorry oval fans, but all the others are just permutations on a theme for me)
Worst Fictional:
Gran Turismo - Cape Ring, Sierra, restyled Grand Valley (squared esses before tunnel), restyled High Speed Ring (banks not steep enough), New Rome (just bleh compared to old one)
Aside from GT there's not really much that springs to mind. Most fictional circuits are just meh, nothing special or bad about them, so I don't have any particularly strong feelings towards them. Also the proliferation of open worlds in arcade games have made it difficult to rate tracks properly (see above).
Well that's it from me. I doubt anyone will read this list in its entirety, but oh well...
