The big thing is salary. Kadri is a great deal for a 2nd line center as long as you're willing to live with his bit of a SNL Superstar mentality and all that comes with it.
Kerfoot is simply a better 3rd line center, with more defense, blocked shots, more hits, zone coverage, penalty-killing. Offensively there's three 5-on-5 points separating them.
To me, Kadri is strictly a 2nd line center where Kerfoot is a hybrid of a 2nd-3rd line player. 3rd line center? Kerfoot is the winner. IMHO, if there's player v.s. player debate
it would be comparing Tavares v.s. Kadri.
There is a certain role you wish your 3rd line center could fill that neither Kadri or Kerfoot bring to the table however. A really good 3rd line center should make the opposition think about retiring from the game. There won't be any fun for them. No scoring. Taking a physical toil, without getting a chance to get on the power-play. If you do get a power-play, they shut it down. Emotionally, leaving you uninspired, sap any emotion or confidence. ...scoring is a secondary concern.