Halo was HUGE. Tbh I don't think either of them are defining hits... the average person would remember it if someone played the song for them, but Halo isn't the first song you think of when it comes to Beyonce, and Stay isn't the first song you think of when it comes to Rihanna
Stay was very big but still quite recent. I still hear Halo used a lot in adverts for TV programmes, on the radio etc. and is one of Bey's memorable hits so I'll choose Halo.
It was so used everywhere, movies, tv shows. Covered by so many artists, 30STM using the cover in their tour. What kind of legendary song. 
