Alton Towers is the British theme park and chock full of roller coasters. A teenager's heaven. They researched it in advance to find the best rides - not something I'd seen them do with, say, the British Museum.
Couple of tips - go in the middle of the week, take warm clothes and avoid the school holidays. There were next to no queues and plenty of rides to chose from in mid Oct.
And don't expect to sit in the cafe. The kids won't let you.