Current agreement best (5)
I believe the answer is:
ideal
'best' is the definition.
('ideal' can be similar in meaning to 'best')
'current agreement' is the wordplay.
'current' becomes 'i' (symbol for electric current).
'agreement' becomes 'deal' (deal is a kind of agreement).
'i'+'deal'='IDEAL'
(Other definitions for ideal that I've seen before include "supreme" , "Conceptual" , "Perfect but perhaps unlikely to become reality" , "Perfectly suited" , "Something that one hopes to attain" .)