Johns comfortably.
Which is no slight really on Lockyer, because he has still been a very good player. If he'd stayed at fullback the arguement would probably be better for him IMO as his defence as a fullback was fine, whilst his attack was obviously very good(altho i still prefer timmy brasher to him).
Johns is a better organiser, better kicking game and has not had the luxury of so many good players around him that Lockyer has, in fact as shown when comparing Newcastle with and without Johns he made a lot of mediocre players look very good.
Added to this is the fact that Johns never needed a lock to run around and protect him in defense. Johns tackled like a second rower. There was a great moment last season in the semi where Brisbane got knocked out by Melbourne, Lockyer rushed up on the storm player and allowed the overlap to develop which lead to that last try. Its those little things, 1%'ers that seperate Johns from Lockyer, he would've read the play better than that which could have prevented the player.
From players i've seen it has to be
Johns>Fittler>Lockyer