This is the big problem with this thread.but I guess it really comes down to what you define as Nas' "prime
Cube had one prime. 88-91. The Predator through Bow Down were dope too, but there was a clear decline.
Nas had at least two primes. Illmatic through IWW. Then he had the awful Firm album and I Am and Nastradamus were uneven to weak, at best. His second peak begins with Stillmatic and extends through the release of the Lost Tapes.
You could even argue a third prime with LIG, but I know I'll lose people with that.
So it's tough to compare these two.