It depends on what you want to do, if you just want to do track days then it doesn't matter really. If you want to Time Attack then AWD is pretty much the way to go, especially in the street tire classes. If you actually want to compete...MIATA

I cant stress this enough, you can buy a Spec Miata that someone else built for very close to that money. Not only are they super reliable but they are good cars to learn in. They will teach you about momentum.

I like Subies but you are going to be pushing that budget to the limit just to swap a STI drivetrain into a coupe. You still won't have suspension or brakes etc...

If you already have a Z06 just track that.