Walker better, but not good (6)
I believe the answer is:
ambler
'walker' is the definition.
(I've seen this before)
'better but not good' is the wordplay.
'better' becomes 'gambler' (a gambler is someone who bets).
'but not' suggests deleting specific letters.
'good' becomes 'g' (abbreviation).
'gambler' with 'g' taken out is 'AMBLER'.
(Other definitions for ambler that I've seen before include "English thriller writer; walker" , "one moving slowly" , "Walker who's rather slow" , "Writer called Eric" , "Eric -, English author (The Mask of Dimitrios)" .)