Modric is Vidal's equal, possibly even narrowly his superior last season, but with a different balance of abilities. He's a better dribbler and more of a game-runner, but much less defensively capable, with less of an engine. In whatever configuration, those two were strides ahead of anyone else last season.
Kroos is probably the third best around at the moment. He's so different it's hard to compare though - Modric and Vidal are both true all-rounders, whereas Kroos isn't really. He can do different roles - the AM or the sitting, string-pulling CM - but he always does one specific job in any given match.
Toure is great but not up there with that lot because he's just too inconsistent. Yes he has lots of great games and is capable of being unplayable sometimes. But those three have all been superb in pretty much every single game they've played this season, whereas Toure still has plenty of very quiet ones.