The coach that will give you the best line-up is probably one with high judging player ability.. But the team they pick also depends on who is performing well in training, it's not necessarily your strongest 11. To look at your best 11 I think you have to go into "Team Report", and even then it's only your assistants opinion of your players.
When I look for an assistant manager I look at:
Tactical Knowledge [for opposition instructions and feedback]
Motivation [For when I can't be bothered to do team talks/ when I am too angry to do team talks]
Judging player ability & Judging player potential [Give me a vague idea of how good the squad is]
Adaptability [pretty sure this effects how quickly somebody gets to know your team]
Determination [Not really sure what this effects but it seems like a good trait to have]
Level of discipline [Don't like my players slacking off!]
& at least 1 high coaching attribute; preferably tactics [Saves me having to hire an extra coach]