Her leading single off the album Red, "We Are Never Ever Getting Back Together," had a heavy hand in the transition of going from the country music space to a more pop-focussed genre. I love a great lyrical puzzle, but it seems like we'll never fully know who she is singing about.
It was her first No. 1 on Billboard's Hot 100, which is a feat in itself, so it only makes sense to be at the top of my list, too. Plus, I can't not dance every time it comes on!