Pokemaniac said:Loopen is, or has traditionally been, TusenFryd's signature ride. Because it has a loop. ThunderCoaster may have taken over since.
I would have guessed Speed Monster would have been the new signature ride, just due to its position in the park. Also being more visible compared to ThunderCoaster which is more hidden away. It seemed to be more popular when I visited and it was the first coaster people headed to when they got into the park.