Honestly the top ten list might just be Illmatic

I'm throwing this together as I write it but here are some of my favourites throughout his career:

• The World is Yours (1994). Great lyrics about self-empowerment, but what makes this classic to me is the complex rhyme schemes and freeform verses that were unparalleled at the time. Might not sound revolutionary now, but that's because everybody's style was informed by this.
• I Gave You Power (1996). A song about inner-city violence as told from a gun's point of view. Nas wasn't the first person to rap from the perspective of a weapon, but I think he did it best. In this era Nas made a mix of conscious rap and (what was then a new form of gangsta rap) Mafioso rap, inspired by flicks like Scarface.
• Nas is Like (1999). This was the weakest year for Nas. He was supposed to release a double album, but after extensive leaks it was mostly scrapped and two albums featuring some fairly weak material were released in its stead. Still, some great songs were in amongst the filler, including this standout.
• Rewind (2001). Another concept track, this time a story told backwards. This is off Stillmatic, which was released after he was dissed by Jay-Z and needed a serious comeback album to save face. It's widely agreed that he succeeded.
• Purple and Doo Rags (2002). The Lost Tapes was a compilation of material that had been scrapped from his 1999 album, and makes it clear that he had been set to release something worthy of his first two albums before it all got nixxed. Pretty much everything off this is strong.
• Last Real N---- Alive (2002). At this time Nas was still fueding with Jay-Z. He's widely considered to have "won" this beef back on Stillmatic, but in my opinion this is a much stronger response than his first. It's a matter-of-fact retelling of his manoeuvres in the rap game and only actually addresses Jay at the end, but the way he establishes context is so effective.
• (He finally released a double album in 2004. It was bloated but had some interesting moments.)
• Fried Chicken featuring Busta Rhymes and Y'all My N----s (2008). This album is officially untitled, but Nas made it clear that it's called N----r and it deals with many topics affecting black people in the US. There are perhaps some misteps in there, but it manages to be profound and entertaining for most of its runtime.
• The Truth (2021). I'm not as familiar with his late career so I don't have so much to add from his last few albums, but they've all been produced by one person (Hitboy) and have a throwback boom bap styles. There's a lot of reflection about his life and quite a lot of bragadoccio, but he's always had an interesting perspective as a disruptive artist.