"It doesn't matter which” (3)
I believe the answer is:
any
'it doesn't matter which' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for any that I've seen before include "Long-running Radio 4 discussion show" , "One, some, every or all without specification" , "A lot < ? Not a lot < -- some" , "One or some, whichever you choose" , "One, no matter which" .)