Just from memory and watching the highlights of both - Shazier was a more dominant, violent hitter with incredible speed - but he also was a victim of over pursuing and missing some tackles.
Darron Lee is a more skilled tackler and wrapped up his opponents solidly - but was not as physical and intimidating as Shazier.
Also keep in mind that Darron Lee benefited a lot from having Bosa and a solid interior DL commanding double teams which freed him up to launch into opponents backfield.
Shazier never had that luxury. Shazier playing on the 2014 team would have been a terror and would have won the Butkus I am sure of it.
IMHO at this stage Sazier >>>Darron Lee.