Drunk In Love. The sales argument is very skewed considering Gaga released Applause as a traditional lead single with a proper promo blitz and Bey didn't even give the single a proper launch until after a million of the album had already been sold. Plus it's had four additional months worth of sales and DiL is still selling.
Also, Drunk in Love wasn't initially sent to pop radio which is the primary digital track buying market -- it just crossed over later after weeks of smashing on urban. Also, DiL was/is incredibly strong with streaming/on demand -- really impressive considering how many people already owned the video that would be driving a lot of those streaming clicks under normal circumstances considering everyone that had the album, owned the video.