Who is more productive and who is better imo is not important discussion.
Unless you are palmer and jackson who we all know not going to be sold, the discussion should be more on who is realistically can be sold.
Felix, sancho, neto were signed last summer, it will be difficult to move them.
Moving Mudyrk, madueke n nkunku are far more realistic. Out of these three, I can see Mudryk being the most difficult to move. Madueke is probably the easiest which is why he was on sale last summer. (Of course all of this still depend on how much is our asking price)