Tsukuba or Road Course Indy for flat track testing depending on how fast the car is. Settings that work here will generally work at Nurb GP/D/F, Monza, Fuji, Lemans etc.
Deep Forest/Deep Forest Reverse/Trial Mountain for twisty, bumpy, cambered corner track testing. Settings other than transmission that work here generally work at the Nurb, Eiger, Trial Mountain Reverse etc.
Grand Valley East is often a track I use to push a car to it's limits as that one downhill section after the esses where you are full out in 5th gear and trying to turn, brake and downshift into 2nd all at the same time, is a real test for a many cars.
I tune pretty quickly so I try to stick to shorter tracks that I can run a couple of laps on under 3 minutes and come in for adjustments.