Picking the best LM car and JGT car is a tough question. But I like the Nissan R390 '97 GT1 LM the best. Best paint, best weight distribution, best looks...a superb all-around car.
It's hard to pick the best JGT car, there's really only about 4 "real" choices (NSX, GT-R, Supra, or STP Viper). I've become partial to the Cerumo Supras lately.
I don't think the ASC and TCS are rather "professional", I think you should experience the way a car handles without driver aids. You can get by without them, if you have a little time to tune cars.