I would say that McDonaugh and Girardi are better than what the Devils have. Staal may be a bit better, but not by much. The Rangers defense drops after McD and Girardi and then again after Staal and MDZ. Devils defense from top-to-bottom is better than the Rangers, but I don't want to get sidetracked here.
If we including goaltending in the definition of "defense" than yeah, Rangers win out easy. If we take just the defenders, then I'd pick the Devils.
There's no drop after McDonagh and Girardi. Staal is arguably better defensively than both of them. The Rangers top 3 is easily better than anything the Devils have right now. MDZ is our 4th best and probably equal to the Devil's best.
After the top 4 the Rangers have a massive drop off, mostly because they don't have a number 6, but that top 4 is overwhelming.
I like the Devils defense because it's deep and I'd still put them top 10 in the league but they can't challenge an elite top 4.