Dark Horse is the better song and will sell a lot more in the end. However, Singles Ladies will forever be iconic because Beyonce ha dancing left the world in amazement.
I remember my 8th grade teacher watching the MV in class and trying to imitate the ring dance. Hew else but King Bey
Regardless of performance with/without video..."Single Ladies" is something that will be remembered for decades to come and that dance is planted in the heads of folks from 6 years old to 106 years old.
Dark Horse is obviously going to be the bigger hit, look at how huger its become without a video, single ladies is more iconic tho, so it depends in the music video of DH on how iconic it can become