I don't know that either guy is truly the one you want anchoring your defence corps as "The Guy". They're both basically Top-3 sort of guys being asked to play as a true #1D. Chychrun looked a lot better when he had OEL there to bear the brunt of things. That's probably where both he and Nurse should be. More of a #2 guy, or a #1b type or something.
I kinda lean toward Chychrun between the two. I think he'd look alright again playing with the Oilers offensive firepower, even if asked to be that #1 on the Oilers blueline.
But you factor in contracts and it's not even a contest.