Top Thrill Dragster & Kingda Ka

These two roller coasters being the fastest on Earth, unfortunately I have not ridden either of them. But I have seen enough documentaries and forum topics about them that have caused me to question. Which is better? Kingda Ka is technically the fastest roller coaster in the world, but I constantly hear about it closing down because of launch failures etc. Top Thrill Dragster isn't quite as fast, and it doesn't have the huge hill before the brakes, yet I hear about how efficient it runs. But I ask the people that have ridden both, which of these do you think is better?

Two words for you: Forum Search.