Decent and fair appraisal from Squawka on the best CB signings of the Summer (Bailly and Matip both come out of it very well) :
http://www.squawka.com/news/compare...-luiz-which-summer-signing-is-the-best/762730
Grujic looks almost good enough to start for us already(not too much competition in CM) ! I can see this lad becoming a star, he's got a lot in his locker so we're hoping he can take the big step up to the PL, though I doubt he will see much game time this season, he looks like one for next.
Impossible to say whether any players will or will not become top players (obviously it's pretty much impossible, unless he is a Messi/Ronaldo/Suarez) to call anyone 'best in their position' but to become a highly rated player is an easier call but still one I'd be reticent to make on any player as so much can go wrong or sometimes they just seemingly come out of nowhere (Mahrez for example).