I don't know about you guys, but judging a young CB has always been my biggest problem in judging players and that's where I made most wrong predictions. That's why I rarely, almost never, make ones.
So many times a solid unit and a solid partner can make a CB look 10 times better than he is and vice-versa.
If you watch a CB more often you can already form an opinion about his qualities, but for younger CBs you watch only from time to time, from month to month, it's not easy to do it.
If Kjaer was a midfielder and showed the performances I've seen of him, I'd have been soooo against Juve signing him. Some serious lack of speed, concentration and aggressiveness is what I saw. But I know how much I suck in judging a CB and I know that he's rated by coaches, so I admit a defeat, for now.
Those who played as CBs in their life can judge a CB easier. Like Red in this forum. But I have a feeling that the majority here is more like me than like Red, and sorry but I won't trust you in these debates Kjaer vs Bonucci vs Subotic vs another young CB, simply because I don't trust myself and I know that most of you suck in this just as much as I do