Lyrically IWW is better but I don't agree at all about the production being better.
I see a lot of Nas fans say they think IWW > Illmatic and I understand it because just in terms of rapping that was Nas at his peak.
But still, Illmatic has a timelessness to it that can't be topped. Every song on Illmatic is a seminal song in hip hop that resonates within the culture, the same isn't true about IWW.
No one outside of diehard Nas fans would ever claim IWW is the best hip hop album of all time whereas Illmatic would be in the shortlist for a lot of rap fans even if they aren't huge Nas fans.
It's a Mt. Rushmore type of album.
It's no different than Kind of Blue by Miles Davis or A Love Supreme by John Coltrane, their may be some aficionados of those artists who think some of their other projects are better than those, but as a whole
Illmatic is a Mt. Rushmore type of album like those. It's an all time great album regardless of genre, IWW doesn't carry that same weight.