Wagner is the best Mike in the league now easily and ha been among the elite of the elite of all football players for a while now. I really like Kuechly as a WLB where his pass coverage ability is maximized and his weakness at the point of attack is minimized. Dude is 6'2/6'3 238. He's light and undersized with an average center of gravity. On top of that he has 30 inch arms, which is almost an oddity among LBs. I still remember his rookie game against the Hawks. Mike Rob literally put him on his back. Paul McCuistan launched him a legitimate 3 yards in the air(5 yards overall). And he got layed out a 3rd time as well.
I think Kuechly is a brillant football player. He's a really nice athlete in most regards to boot, but I would expect that he had high grades in mathematics and geometry. His use of angles is probably unmatched. However, the use of angles is a byproduct of a weakness against the Point Of Attack.
The single, lone area that Kuechly has an edge on Wagner is pass coverage, but Kuechly isn't even second in any other category. Many LBs are better than him in basically ever other category other than pass coverage. Obviously not understated, but whatever. Wagner is by far the top overall LB in the entire league.