Preferably the artist on the right (6)
I believe the answer is:
rather
'preferably' is the definition.
(I know that preferably can be written as rather)
'artist on the right' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'on' means one lot of letters go next to another.
'right' becomes 'r' (common abbreviation).
'ra'+'the'+'r'='RATHER'
'the' is the link.
(Other definitions for rather that I've seen before include "with more justification" , "On the contrary or to some extent" , "somewhat > sooner? > Quite" , "Most certainly" , "Slightly, more so than not (6" .)