'Bleeding Love'
It's a timeless, modern day classic.
Just an incredible debut, a lyrical masterpiece, bash on Ryan Tedder all you want, but not for this song, his breakout as a songwriter and producer. And bought to life by Leona's soulful vocals, with incredible range and emotion
Biggest seller in the world of 2008

Biggest seller in the UK in 2007
Saying this, I prefer 'Happy', it may not be as catchy, as it doesn't have the hook that 'Bleeding Love' has, but it's much more Leona, it's embodies her.