Nas is just better.
Tbh I find lines like "Jay-Z picks amazing beats" and "Jay-Z is consistent" just regurgitated cliches.
You could put their albums against each other and Nas would come out on top, even a Jay-Z fan couldn't say Jay-Z has had more than 3 good albums. Nas has had more than 3, so I don't buy the consistency argument at all.
Nas doesn't try to pick the most structured or technical beats because that's not the sort of rapper he is.
NaS - Halftime (complete with lyrics) - YouTube
Undoubtedly a classic but the beat is very simple, it doesn't mean it's poor though, and it allows Nas to play to his strengths. Jay-Z has no strengths as a rapper, relies on the beats to carry his tracks. He's a jack of all trades master of nothing.