Depends on what you’re looking to do to the car. Your car can fit in FS, STU, and CAM-C.
If you plan on leaving it alone, you’ll get a significantly better PAX in FS.
If you plan on modifying it within the year, you’ll probably be better served in CAM-C due to the very loose rules.
I wouldn’t put the car in STU. It’s got a worse PAX than CAM-C and the rules are more restrictive.
FS will have more competitors, but your car will never be competitive against them (short of maybe older mustangs/camaros).
If it were me, I’d go CAM-C.