Coldplay have sold over 100 million records and built one of the most devoted fanbases in music — and the debate over their greatest song reflects the breadth of their career. The Scientist is their most emotionally devastating ballad — a song about regret and the impossibility of undoing mistakes that has made millions of people cry. Fix You is their most consoling song, a piece of music so precisely calibrated to comfort grief that it has been played at thousands of funerals and memorials around the world. Yellow was their breakthrough — a love song of such simple beauty that it launched one of the biggest careers in British music. Clocks won them the Grammy for Record of the Year and remains their most musically sophisticated song. A Sky Full of Stars showed they could make stadium anthems without losing their emotional core. Which Coldplay song is truly their greatest?