Mag was our best defender. Cliff was our most important defender. Caleb was known as our best defender.
Mag led the press and was a great onball defender. Caleb's defense took a small step backwards last year. Mag was a better on ball defender against most players. Caleb was more destructive in a help position in the half court causing turnovers. He definitely masked Paul and Cam's deficiencies with lateral quickness, bailing them out.. Gavin would have DEFINITELY benefited having Caleb.
Mag was a better on-ball defender against frontcourt players, and McConnell was better against backcourt players. That also led to McConnell picking up more steals, because he was harassing ball handlers and disrupting passing lanes between guards. Mag was better bodying post players than McConnell.
They both had the ability to switch onto pretty much anyone... but McConnell was better switching 1-4 defensively (especially the 2/3 roles), and Mag was better switching 2-5 (especially the 3/4 roles). McConnell generally drew the #1 non-center defensive assignment each game and was a bit more important to be on the floor (and saw more minutes per game).
They both were plus help defenders, but McConnell had an edge there. Mag was a better press defender and had an uncanny ability to just be in the right place at the right time to spring traps.
If Mag had continued to develop uninterrupted last year, I feel he could have surpassed McConnell by the final handful of games... he was really growing more and more into that defensive role as the season wore on.