We had a bunch of high schoolers visit the campus I work at. The basement of the Union has McDonalds, Blimbie, Sbarro, and a Sushi joint. I would estimate 90% ate at McDonalds, 6% at Blimpie, 4% at Sbarro, and 0% at the Sushi joint.
Your percentages on how many teens ate at each place sound spot on. Teens don't are about healthiness of a food. They are all about mass quantity, flavor, and cost.