I think Willis was a far more polished product, more game ready than most prospects in recent memory, better at the point of attack, fighting through blockers, better overall instincts.
Jack is more a "jack of all trades" type, better suited for coverage but gets washed out a lot going against blockers. Coverage-wise I think he'd be a top 3 LB in the NFL from day one. For as big as he is, he's shown the ability to hang with WR's, let alone TE's and RB's. In that regards he'd be the ultimate dream fit for a Tampa 2 scheme. Teams have tried him out at safety so he'd be a very versatile guy that could be used in a number of ways by a creative defensive coordinator.
I could see his upside being a Derrick Brooks type of LB, although even faster but he's still fairly raw at this point.
[ Edited by Phoenix49ers on Apr 9, 2016 at 11:03 AM ]