Semi you are mostly correct.
At Bondurant, the Mustangs are Cobras and GT's and are a blast to drive. You get quality time with an instructor showing you how its done then sitting beside you while you drive. The fourth day is actually a Forula Ford with wings. They call it "F1 style" for advertising purposes. The cars are fast and a blast also.
Bertil Roos has a good school in the Northeast somewhere (I don't remember where exactly, but I think Nazareth, PA) and uses Formula 2000 cars. Justin Bell is at Virginia Intl Raceway and uses Corvette Z06's. Skip Barber is average at best. Derek Daly's school in Vegas is good but high-priced. Then you have all of the driving experiences (CART Driving 101, Richard Petty, etc.).
The bottom line is: what do you want to learn and what types of cars?
For all-around learning, Semi is right on. Go to Phoenix and make a vacation out of it. You can't miss with Bondurant.