V6 because :
Cheaper insurance, first cars with young drivers mean highest insurance rates. And the V8 makes it the most expensive.
Limited driving experience. The Mustang is a lightwieght rear wheel drive car. The higher torque and horsepower may to much to handle. I had a V6 rent-a-car and punched it in the rain with a right hand turn. I did a 720, two complete revolutions.
Better gas mileage, helping save money.
Youth, with the curiousity to see what the car will do, testing it.