Pick clubs and hearts over diamonds (6)
I believe the answer is:
Here is my best explanation:
'pick' is the definition.
('choice' can be a synonym of 'pick')
'clubs and hearts over diamonds' is the subsidiary indication.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'and' means one lot of letters go next to another.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'over' becomes 'o' (cricket abbreviation**).
'diamonds' becomes 'ice' (I've seen this before).
(Other definitions for choice that I've seen before include "act", "Will", "'Selection, option (6)'", "Act or power of selecting", "of superior quality", "Preference", "Very good", "Superior - selection", "'Option, alternative (6)'" and "Sophie's ---, William Styron novel".)