Best work men? (7)
I believe the answer is:
optimal
'best' is the definition.
(optimal means the best)
'work men?' is the wordplay.
I cannot really understand how this works, but
'work' could be 'op' (abbreviation for opus) and 'op' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for optimal that I've seen before include "top, surprisingly" , "Am pilot being at best" , "Most favouring" , "as good as can be" , "couldn't be better" .)