Choice of letter size for keyboarder (5)
I believe the answer is:
elite
This clue is a double definition.
'choice' is the first definition.
(I've seen this before)
'letter size for keyboarder' is the second definition.
(size of letter on typewriters)
'of' acts as a link.
(Other definitions for elite that I've seen before include "Group considered to have superior status" , "Exclusive group" , "twelve pitch in the office" , "Superior group in society" , "Group enjoying superior status" .)