It's a tough call. Milner is probably my favourite player for us at the moment and alongside the fantastic work ethic is attacking prowess, good technique and consistency.
However, Young on his day is as MON said a 'genius' - he can skin people left, right and centre, can play a killer ball in, has great pace and can be genuinely unplayable at times.
I went for Young but Milner isn't that far behind whatsoever.
We should be thankful that we have both and Downing, Albrighton and The Cannon also!