You're never going to find a best all-around road course car. If there were such a thing, everyone with brains would be driving it.
There was a thread created within a month or two ago about the E46 M3's and someone summed the car up quite well. He said something along the lines of, "The car doesn't do one thing extraordinarily good, but it does everything very well." Out of your list I think the E46 M3 would be my first choice. Anything mid-engine isn't going to be the best for someone trying to pick up road course racing, as they can be very finicky as far as control. IMO, anything 4WD doesn't always make the best road course cars either. Usually they exhibit a tendency to understeer which isn't something you want to deal with. I would try to find something well balanced and RWD.. so out of your list the Z06 and the M3s appeal most to me.
Honestly, if you could find an LSx swapped FD.. you'd have a perfect road course car. VERY well balanced machines paired with a LSx motor that's actually lighter and more reliable than the 13b when beaten on and you're in a good position to learn how to control and balance your vehicle without worrying about much else. Finding a car that suits your needs in stock form is ideal too. You really want to focus on learning the cars limits in stock form in the beginning and then step up your suspension and power as you learn how to control and toss around weight and use power to your advantage.
I'll just stop there, I could probably go on forever about this and that.. but I think you should consider something your most confident and comfortable with.