I'd pick NM based on today, but it gets interesting with Matthews based on their numbers in their first four seasons (which Matthews is in now.)
His first four seasons MacK topped out at 63 points and only had 53 in 16-17 (his fourth season.) Matthews lowest point totals in his first 4 seasons, including this one, is 63, and he currenty has 68 in 57 games (his fourth season.)
MacK blew up after that and has been a near 100-point player since 97, 99, and currently has 76 in 54.)
I think it's likely Matthews makes his way into 90 points in his 5th and 6th seasons (good chance at doing it this season,) however MacK has already done it, so I take proof over potential.
Its also interesting, due to their birthdays, even though NM is "3 seasons older" than AM, he's only 2 years older by actual age. So depending on how you value pre-NHL experience, you could compare AM's season this year to NM's 17-18 season (5th seasons.)
As a sidenote, I still chuckle at a handful of posters who were calling MacK a bust a few years ago. Props to Avs fans for staying faithful.