single duh. a #1 single is a success 90% of the time. albums are about overall sales not peaks. albums that peaked at #15 can be more successful than a #1 album
Singles. Having a #1 single is too difficult. For having a #1 album, you need just a very good lead single and promo. But having both(e.g. PRISM, Roar, DH) it's way more better.
Atm a single because some people are getting a #1 with less than 100k(Ariana,Selena and all of those kind of singers)
But you should add to the poll sales because those are way more important than a #1