Big was undeniably more popular but I also think Big had a MUCH better team behind him. Clive Davis AND puff. Think about that. Davis made Whitney Houston and a whole string of other amazing artist since the 70s. And puff knows how to make hits. With illmatic, Nas had his own raw talent / X factor, mc serch

and some Columbia clowns. Not even close there.
Biggie naturally connected to wider audiences though anyway, but it was multiplied by the fact the industry was pushing him in a way they weren't or couldn't with nas. Biggie had that X factor too but it was just amplified by insanely good marketing.
I think if nas died a week before IWW, he'd be remember as the biggest What If. Pac and biggie died at the height. Nas would have been remembered as a great that never got to reach what people thought was his peak. shyt people still waiting for the album everyone thinks he's capable of even after all this time. But we wouldn't have to look past albums like Nastradamus and SD. Hed be above Big L and Pun, but not as enshrined as pac and big.