As in "BEST" you must mean for the best clubs in the world, because they have the best managers, and assistant managers. The rest all depends on what you're looking for in your team, or even more more importantly WHERE you are playing and with WHAT team. It's a hard question to answer, and like most tactic,staff,player,training questions and threads....it changes from staff,to player, to team, to league, to nation, to personal choice, just like music and ice cream. (but if you "need" help, the higher the rating in their specific choise of job, the better they are at it.)